A high-efficiency short-flow preparation method of a Φ1200mm and above super-large caliber G115 heat-resistant steel seamless pipe

Abstract

A kind of high-efficiency short-process preparation method of Φ1200mm and above super-large caliber G115 heat-resistant steel seamless pipe, comprising: 1) blank preparation, electric furnace steelmaking+electroslag remelting is adopted to obtain electroslag round ingot, the specification is diameter ≥Φ900mm, length 1500~3000mm;2) backward extrusion piercing, three-stage heating is adopted, slow cooling to room temperature after extrusion is completed, demoulding;3) positive extrusion hole expansion, three-stage heating is adopted, and the blank is positively extruded, and the positive extrusion speed is 5~50mm / s;After extrusion is completed, air cooling to room temperature;The extruded G115 steel pipe is stress relieved annealing, two-stage heating is adopted, and the furnace is cooled to 300~500 DEG C after annealing is completed and discharged;4) quenching and tempering heat treatment, quenching treatment, austenitizing temperature 1030~1100 DEG C, holding time 2~7h, water cooling;Tempering treatment, tempering temperature 750~800 DEG C, tempering time 4~10h, air cooling.

Description

Technical Field

[0001] This invention belongs to the field of steel material processing technology, and relates to an efficient and short-process preparation method for ultra-large diameter G115 heat-resistant steel seamless pipes with diameters of Φ1200mm and above. Background Technology

[0002] Against the backdrop of accelerated energy structure transformation and large-scale development of clean energy, large-scale energy equipment such as thermal power generation and advanced supercritical units are rapidly evolving towards higher parameters, larger capacity, and higher efficiency. This places urgent demands on the material properties and manufacturing capabilities of key high-temperature pressure-bearing components.

[0003] G115 martensitic heat-resistant steel has significantly better high / high temperature tensile properties, impact properties, creep strength, steam oxidation resistance, and structural stability than traditional materials such as P92 steel. It is especially suitable for core components such as main steam pipes of ultra-supercritical units at 630℃ and above, and is an important foundation for ensuring the safe and economical operation of the next generation of efficient and clean coal-fired power plants.

[0004] However, with the continuous increase in the capacity of thermal power generation units, the diameter requirements of key components such as main steam pipes have exceeded Φ1200mm. The traditional long-process preparation method of "ingot forging + piercing + multi-pass hot rolling" has exposed technical problems such as lengthy process, serious material loss, high manufacturing cost, long cycle and low yield when facing such ultra-large diameter, high-performance seamless pipes. These problems seriously restrict the further large-scale application of G115 heat-resistant steel and the rapid upgrading and deployment of energy equipment. Summary of the Invention

[0005] The purpose of this invention is to provide a highly efficient short-process manufacturing method for ultra-large diameter G115 heat-resistant steel seamless pipes with diameters of Φ1200mm and above. This method enables the efficient and stable short-process manufacturing of ultra-large diameter G115 heat-resistant steel seamless pipes with diameters of Φ1200mm and above. The properties of the manufactured pipes meet the requirements of standards such as T / CSTM 00017-2021 and Q / OAPD 2253-2022, including room temperature tensile strength ≥660MPa, yield strength ≥480MPa, elongation ≥16%, impact energy KV2 ≥27J, and Brinell hardness between 195 and 250HBW.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A highly efficient, short-process method for manufacturing ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above includes the following steps: 1) Billet preparation Electroslag round ingots are obtained by electric furnace steelmaking followed by electroslag remelting, with a diameter ≥ Φ900mm and a length of 1500~3000mm. 2) Reverse extrusion perforation A three-stage heating and holding method is adopted. The first stage heating temperature is 600~850℃, and the heating and holding time is 5~8 hours. The second stage heating temperature is 1000~1100℃, and the heating and holding time is 7~11 hours. The third stage heating temperature is 1180~1280℃, and the heating and holding time is 13~20 hours. The heating rate is ≤150℃ / min, and the heating rate gradually decreases as the heating temperature increases. The total heating time is ≥25 hours. Then, it is subjected to reverse extrusion piercing in a vertical extrusion press with an extrusion pressure of 270~325MN and a reverse extrusion speed of 10~50mm / s. The specifications of the tube blank after reverse extrusion are outer diameter Φ1200~Φ1800mm × inner diameter Φ300~Φ500mm. After extrusion, it is slowly cooled to room temperature and then demolded. 3) Positive extrusion reaming A three-stage heating process is adopted: the first stage heating temperature is 500~750℃, and the heating and holding time is 5~9 hours; the second stage heating temperature is 1000~1100℃, and the heating and holding time is 7~11 hours; the third stage heating temperature is 1180~1280℃, and the heating and holding time is 13~20 hours. The billet is then subjected to positive extrusion in an extruder with an extrusion pressure of 375~425MN and a positive extrusion speed of 5~50mm / s. After positive extrusion, the specifications of the G115 steel pipe are an outer diameter of Φ1200~Φ1800mm × a wall thickness of 40~250mm. After extrusion, the pipe is air-cooled to room temperature. The extruded G115 steel pipes are subjected to stress-relief annealing using a two-stage heating process. The first stage heating temperature is 400~600℃, and the heating and holding time is 4~9h. The second stage heating temperature is 750~800℃, and the heating and holding time is 11~14h. After annealing, the pipes are cooled in the furnace to 350~500℃ before being removed from the furnace. 4) Tempering heat treatment Quenching treatment, austenitizing temperature 1030~1100℃, holding time 2~7h, water cooling; Tempering treatment, tempering temperature 750~800℃, tempering time 4~10h, air cooling.

[0007] Preferably, step 2) involves loading the furnace into a cold furnace or a furnace with a temperature ≤500℃.

[0008] Preferably, in step 2), the heated billet is transferred to a mechanical descaling machine to remove the oxide scale. After descaling, it is returned to the furnace for a short period of reheating to 1180~1280℃ for 20~50 minutes.

[0009] Preferably, the billet forming cylinder and mandrel are preheated to ≤500°C before the electroslag round ingot is discharged from the furnace, and graphite emulsion is sprayed inside the billet forming cylinder and on the surface of the mandrel. After the electroslag round ingot is discharged from the furnace, glass lubricating powder is sprayed on the upper surface and the outer circumference.

[0010] Preferably, step 3) involves loading the furnace into a cold furnace or a furnace with a temperature ≤500℃.

[0011] Preferably, in step 3), the heated billet is transferred to a mechanical descaling machine to remove the oxide scale. After descaling, it is returned to the furnace for a short period of reheating to 1180~1280℃ for 20~50 minutes.

[0012] Preferably, in step 3), before the tube blank is extruded, the extrusion cylinder, extrusion die and mandrel are preheated to a temperature of ≤500℃. At the same time, graphite emulsion is applied to the surface of the die to reduce friction. After the tube blank is taken out of the furnace, glass lubricating powder is sprayed on the inner and outer surfaces.

[0013] Preferably, step 3) annealing is performed by loading the furnace into a cold furnace or loading the furnace at a temperature ≤500℃.

[0014] Preferably, after annealing in step 3), the material is transferred to a horizontal pressure straightening machine for three-point pressure straightening to ensure that the curvature is ≤3mm / m.

[0015] In the efficient short-process preparation method of ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above described in this invention: Step 1) In billet preparation, a dual-process casting technique of "electric furnace steelmaking + electroslag remelting" is used to obtain high-purity, high-uniformity, and high-density G115 heat-resistant steel billets, thus providing high-quality billets for subsequent efficient short-process manufacturing. The billet specifications are electroslag round ingots with a diameter ≥ Φ900mm and a length of 1500~3000mm. Before proceeding to the next process, the electroslag round ingots are machined and partially ground to a bright finish; subsequently, flaw detection is performed to determine the length of the billet round ingot; simultaneously, the macro- and microstructure, grain size, and chemical composition of the head, tail, and length directions are inspected.

[0016] Step 2) In the reverse extrusion piercing process, the electroslag round ingot G115 steel is heated and held in three stages to ensure uniform temperature. The final holding temperature is 1180~1280℃, and the total heating time is ≥25h. Specifically, the first stage heating temperature is 600~850℃, and the heating and holding time is 5~8h; the second stage heating temperature is 1000~1100℃, and the heating and holding time is 7~11h; the third stage heating temperature is 1180~1280℃, and the heating and holding time is 13~20h.

[0017] Because G115 steel is a martensitic heat-resistant steel, to prevent cracking of G115 steel electroslag ingots due to thermal shock, a cold furnace or a lower temperature is used for charging, and the heating rate does not exceed 150℃ / min. As the heating temperature increases, the heating rate gradually decreases to ensure temperature uniformity inside and outside the ingot. Simultaneously, to address the problem of easily segregating elements such as W forming coarse tungsten-rich phases, G115 steel electroslag ingots require high-temperature, long-term diffusion treatment. Therefore, the total heating time is ≥25 hours to dissolve the coarse segregated phases and improve the homogeneity of the ingot. Subsequently, the heated billet is transferred to a mechanical descaling machine to remove oxide scale. After descaling, it is returned to the furnace for a short-term reheating to 1180~1280℃ for 20~50 minutes. The purpose of this short-term reheating is to eliminate the temperature difference between the surface and core of the billet caused by descaling.

[0018] Before the electroslag ingots exit the furnace, the billet forming cylinder and mandrel are preheated to ≤500℃, and graphite emulsion is sprayed inside the billet forming cylinder and on the surface of the mandrel. After the electroslag ingots exit the furnace, glass lubricating powder is sprayed on the upper surface and the outer circumference. Finally, the billet after the reheating is completed is transferred to a 10,000-ton vertical extrusion press for direct reverse extrusion piercing. The billet transfer should be rapid and the time should be controlled within 300 seconds. After extrusion, the billet is slowly cooled to room temperature and then demolded.

[0019] The extrusion pressure is 270~325MN, and the reverse extrusion speed is 10~50mm / s. The extrusion speed should be kept stable throughout the reverse extrusion process to ensure stable metal flow and reduce tail defects. Slow cooling aims to prevent the billet from cracking due to martensitic phase transformation and to eliminate thermal and structural stresses. The billet specifications after reverse extrusion are an outer diameter of Φ1200~Φ1800mm × an inner diameter of Φ300~Φ500mm. The inner and outer surfaces of the cooled billet are machined or ground to a bright finish to thoroughly remove surface oxide scale, cracks, etc.

[0020] Step 3) During the positive extrusion reaming process, the G115 steel billet is heated in three stages, with a final holding temperature of 1180~1280℃ and a total heating time of ≥25h. Specifically, the first stage heating temperature is 500~750℃, with a heating and holding time of 5~9h; the second stage heating temperature is 1000~1100℃, with a heating and holding time of 7~11h; and the third stage heating temperature is 1180~1280℃, with a heating and holding time of 13~20h.

[0021] The tube blanks are fed into the furnace at a cold temperature or low temperature to prevent cracking caused by thermal shock. Subsequently, the heated tube blanks are transferred to a mechanical descaling machine to remove the oxide scale. After descaling, they are returned to the furnace for a short period of reheating to 1180~1280℃ for 20~50 minutes.

[0022] Before the tube blank is extruded, the extrusion cylinder, extrusion die, and mandrel are preheated to ≤500℃. Simultaneously, graphite emulsion is applied to the die surface to reduce friction. After exiting the furnace, glass lubricant powder is sprayed onto both the inner and outer surfaces of the tube blank. Finally, the preheated blank is transferred to a 50,000-ton extrusion press for direct extrusion, and then air-cooled to room temperature after extrusion. The tube blank should be transferred rapidly after each furnace exit, with the transfer time controlled within 300 seconds.

[0023] The extrusion pressure is 375~425MN, and the positive extrusion speed is 5~50mm / s. The extrusion speed should be kept stable to ensure stable metal flow. The specifications of the black tube after positive extrusion are: outer diameter Φ1200~Φ1800mm × wall thickness 40~250mm.

[0024] The extruded G115 steel black-skinned pipes are transferred to a bogie hearth furnace for stress-relief annealing. The annealing process involves cold furnace loading or loading at a furnace temperature ≤500℃, using a two-stage heating method to 750~800℃, with a total heating time ≥15h. Specifically, the first stage heating temperature is 400~600℃, with a heating and holding time of 4~9h, and the second stage heating temperature is 750~800℃, with a heating and holding time of 11~14h. After extrusion, the pipes are loaded into the furnace at a cold temperature or low temperature to prevent cracking caused by thermal shock. After holding, the pipes are cooled in the furnace to below Ac1 (300~500℃) and then quickly transferred to a horizontal pressure straightener for three-point pressure straightening, ensuring that the curvature is ≤3mm / m. During the straightening process, the single-point reduction and total deformation are controlled.

[0025] Step 4) In the quenching and tempering heat treatment, the G115 steel black-skinned pipe undergoes quenching and tempering, i.e., quenching + high-temperature tempering. Quenching and tempering is a prerequisite for obtaining a stable microstructure, ensuring that the type, size, and distribution of precipitates in the G115 steel reach their optimal state, thereby guaranteeing the long-term high-temperature service of G115 steel. At the same time, it can ensure the uniformity of microstructure and properties in the wall thickness direction of large-diameter pipes.

[0026] The purpose of quenching is to transform high-temperature austenitic structures into lath martensite with high dislocation density through rapid cooling, and to achieve uniform cooling inside and outside thick-walled tubes, thereby obtaining a uniform martensitic structure across the entire cross-section. Controlling the quenching cooling rate ensures that the cooling rate at the center of the tube wall thickness is higher than the critical cooling rate of G115 steel, and avoids the formation of non-martensitic structures.

[0027] The purpose of high-temperature tempering is to ensure that quenching stress is fully eliminated to prevent cracking, and to ensure that a large number of fine carbides and other precipitates are dispersed in the martensitic matrix and uniformly formed across the entire tube wall cross-section. Therefore, the tempering time needs to be long enough. On the other hand, high-temperature tempering can obtain a stable tempered martensite structure, ensuring high strength while achieving excellent plasticity and toughness.

[0028] Finally, the inner and outer surfaces of the black-skinned pipes, cooled to room temperature, are machined or polished to a glossy finish to completely remove surface oxide scale, etc., ensuring that the length, wall thickness, roundness, etc., meet the technical requirements.

[0029] Compared with the prior art, the present invention has the following beneficial effects: 1. The traditional manufacturing process of G115 steel seamless pipes requires four major steps: smelting, forging, hot rolling or extrusion, and quenching and tempering. In particular, the forging process involves multiple heating, upsetting or drawing, and intermediate treatment (such as grinding), which makes the process lengthy and the production cycle slow.

[0030] This invention employs a "reverse-forward extrusion" short-process technology, integrating the main forming process into a continuous extrusion step. This eliminates repeated upsetting and drawing forging processes, reducing the total number of steps by approximately 25% and enabling efficient forming of ultra-large diameter G115 steel pipes. This not only significantly shortens the production cycle but also improves equipment utilization and capacity. Furthermore, by reducing the number of heating passes, it significantly reduces energy consumption and carbon emissions, aligning with the trend of green manufacturing.

[0031] 2. Traditional processes suffer from severe material loss, with the yield from steel ingots to finished pipes typically only reaching 50-60%.

[0032] The extrusion process employed in this invention is a near-net-shape forming technology, which can increase the material utilization rate from steel ingot to finished tube to over 70%, resulting in significant economic benefits. More importantly, the deformation during the reverse extrusion stage, under triaxial compressive stress, effectively breaks down the coarse as-cast structure, eliminates internal porosity, and achieves high density in the tube blank. Subsequent forward extrusion further refines the grains and optimizes fiber flow, significantly improving the uniformity of the microstructure, consistency of mechanical properties, and impact toughness across the entire wall thickness of the tube. This is crucial for the reliability of ultra-large diameter components subjected to high temperatures and pressures.

[0033] 3. This invention employs an extrusion process, particularly reverse extrusion, which can form ultra-large diameter tube blanks with relatively small extrusion pressure. Through precise control of extrusion process parameters, it can achieve stable control of the dimensional accuracy, wall thickness uniformity, and internal and external surface quality of ultra-large diameter tubes, effectively avoiding problems such as center defects that are easily generated in traditional tube rolling. This provides a new feasible path for manufacturing high-performance, high-reliability extreme specification heat-resistant steel components.

[0034] 4. Traditional methods for producing hot-rolled tubes with a diameter of Φ1200mm or larger require heavy equipment, such as a 10,000-ton hydraulic press for billet forging and a 10,000-ton rolling mill with a main motor power of 5000KW or more. This involves huge investments and extremely high technical barriers. This invention uses an extrusion process, especially reverse extrusion, which can form ultra-large diameter tube blanks with relatively small extrusion pressure, reducing reliance on extremely heavy equipment. Attached Figure Description

[0035] Figure 1 Photograph of the tube blank (electroslag ingot) used for G115 extrusion in an embodiment of the present invention; Figure 2 Photograph of G115 steel tube billet after reverse extrusion according to an embodiment of the present invention; Figure 3 This is a photograph of the black-skinned G115 steel pipe after positive extrusion, according to an embodiment of the present invention. Figure 4 This is a photograph of the machined G115 pipe according to an embodiment of the present invention; Figure 5 This is a photograph showing the microstructure of the G115 pipe according to an embodiment of the present invention. Detailed Implementation

[0036] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0037] The process parameters of the embodiments of the present invention are shown in Tables 1 to 4. Table 5 shows the inclusions in the embodiments, and Table 6 shows the mechanical properties of the G115 ultra-large diameter pipe in the embodiments.

[0038] Example 1 A highly efficient, short-process method for manufacturing ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above includes the following steps: 1) Billet preparation G115 heat-resistant steel electroslag remelting round ingots were obtained using a dual-process casting method of "electric furnace steelmaking + electroslag remelting," with specifications of Φ1300mm in diameter × 1800mm in length. Figure 1 As shown; Specifications of the machined and partially ground blank: Diameter Φ1250mm × Length 1650mm; 2) Reverse extrusion perforation The finished G115 steel electroslag round ingots were heated and held in three stages. The furnace was initially cold-loaded. The first stage heating temperature was 600℃, and the holding time was 7.5 hours. The second stage heating temperature was 1000℃, and the holding time was 10 hours. The third stage heating temperature was 1270℃, and the holding time was 20 hours. After holding, a mechanical descaling machine was used to remove the oxide scale. After descaling, the ingots were returned to the furnace for reheating for 20 minutes. Simultaneously, the billet cylinder and mandrel were... Preheat to 400℃, and spray graphite emulsion inside the billet cylinder and on the mandrel surface. After the electroslag ingot exits the furnace, spray glass lubricating powder on the upper surface and outer circumference. Finally, after the reheating is completed, the billet is transferred to a 10,000-ton vertical extrusion press for direct reverse extrusion piercing, with a transfer time of approximately 240 seconds. After slow cooling to room temperature, demold. The extrusion pressure is 270MN, and the reverse extrusion speed is maintained at 12mm / s. The billet specifications after reverse extrusion are outer diameter Φ1790 × inner diameter Φ500mm. Figure 2 As shown; the inner and outer surfaces of the tube blank cooled to room temperature are machined or ground to a bright finish; 3) Positive extrusion reaming The finished G115 steel pipe billet is heated in a three-stage heating method. It is loaded into the furnace in a cold furnace. The first stage heating temperature is 500℃ and the heating and holding time is 8 hours. The second stage heating temperature is 1000℃ and the heating and holding time is 10.5 hours. The third stage heating temperature is 1270℃ and the heating and holding time is 20 hours. The heated billet is transferred to a mechanical descaling machine for descaling, then briefly reheated to 1270℃ for 30 minutes. Before forward extrusion, the extrusion cylinder, die, and mandrel are preheated to 450℃, and graphite emulsion is applied to the die surface. After exiting the furnace, glass lubricant powder is sprayed onto both the inner and outer surfaces of the billet. Finally, the reheated billet is transferred to a 50,000-ton extrusion press for direct forward extrusion and cavitation expansion. After extrusion, it is air-cooled to room temperature before demolding. The transfer time after exiting the furnace is approximately 240 seconds; the extrusion pressure is 376MN, and the forward extrusion speed is 10mm / s. The specifications of the black tube after forward extrusion are: outer diameter Φ1800mm × inner diameter Φ1275mm. Figure 3 As shown; G115 steel black-skinned pipes are transferred to a bogie hearth furnace for stress-relief annealing. The black-skinned pipe billets are cold-charged into the furnace and heated in two stages. The first stage heating temperature is 450℃, and the heating and holding time is 9 hours. The second stage heating temperature is 800℃, and the heating and holding time is 14 hours. After the holding time is completed, the billets are cooled to 500℃ in the furnace and then quickly transferred to a horizontal pressure straightening machine for three-point pressure straightening. After multiple passes of straightening, the curvature is 2.5 mm / m. 4) Conditioning and tempering Quenching treatment, austenitizing temperature 1100℃, holding time 6h, water cooling; Tempering treatment, tempering temperature 800℃, tempering time 10h, air cooling; 5) Finishing The inner and outer surfaces of the black-skinned pipes, cooled to room temperature, are machined or ground to a bright finish. The specifications are: outer diameter Φ1790mm × wall thickness 250mm. Figure 4 As shown; 6) Tissue performance testing The finished bright tubing was subjected to physical and chemical tests at designated locations according to technical requirements and standards, including macro- and micro-structure and mechanical properties. The test results are shown in Tables 5 and 6. Figure 5 .

[0039] As shown in Table 5, the present invention can obtain G115 steel pipes with high purity, and the inclusions of fine and coarse categories A, B, C, and D, as well as inclusions of category DS, all meet the standard requirements, of which inclusions of category A, C, and DS are all grade 0.

[0040] As shown in Table 6, the room temperature tensile properties of the pipes prepared by the technology of this invention are all better than the standard requirements. Specifically, the yield strength is more than 120 MPa higher than the standard requirement, the tensile strength is more than 89 MPa higher than the standard requirement, the elongation exceeds the standard requirement by about 9%, and the impact energy far exceeds the standard requirement, reaching more than 150 J.

[0041] Furthermore, after comparing the mechanical properties (yield strength ≥ 440 MPa, tensile strength ≥ 620 MPa, elongation ≥ 20%) of P92 steel seamless pipe, it was found that the G115 steel pipe prepared by this invention has better overall performance.

[0042] Depend on Figure 5 It is known that the microstructure of G115 steel pipe after quenching and tempering is typical tempered martensite, exhibiting typical needle-like or lath-like morphologies. These martensite morphologies are intertwined, and the tempering treatment releases the stress inside the martensite. At the same time, changes such as the precipitation of carbides may occur in the microstructure. This microstructure has an important influence on the mechanical properties of G115 steel pipe, such as strength and toughness, enabling it to meet the corresponding application requirements under high temperature and high pressure conditions.

[0043] Example 2 A highly efficient, short-process method for manufacturing ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above includes the following steps: 1) Billet preparation G115 heat-resistant steel electroslag round ingots were obtained using a dual-process casting of "electric furnace steelmaking + electroslag remelting" with a diameter of Φ950mm × length of 2300mm; the specifications of the machined and partially ground billet were: diameter of Φ900mm × length of 2100mm. 2) Reverse extrusion perforation The finished G115 steel electroslag round ingots were heated and held in three stages. The furnace was loaded at 500℃. The first stage heating temperature was 850℃, with a holding time of 6 hours; the second stage heating temperature was 1050℃, with a holding time of 8 hours; and the third stage heating temperature was 1200℃, with a holding time of 14 hours. After holding, a mechanical descaling machine was used to remove the oxide scale. After descaling, the ingots were returned to the furnace for reheating for 20 minutes. Simultaneously, the billet cylinder and mandrel were preheated to 300℃. Graphite emulsion is sprayed inside the billet cylinder and on the mandrel surface. After the electroslag ingot exits the furnace, glass lubricating powder is sprayed on the upper surface and the outer circumference. Finally, the billet after the reheating is completed is transferred to a 10,000-ton vertical extrusion press for direct reverse extrusion piercing, and the billet transfer time is about 210 seconds. After slow cooling to room temperature, it is demolded. The extrusion pressure is 307MN, and the reverse extrusion speed is maintained at 45mm / s. The billet after reverse extrusion has an outer diameter of Φ1290×inner diameter of Φ350mm. The inner and outer surfaces of the billet after cooling to room temperature are machined or ground to a bright finish. 3) Positive extrusion reaming The finished G115 steel pipe billet is heated in three stages. The furnace is loaded at a temperature of 500℃. The first stage heating temperature is 750℃ and the heating and holding time is 5.5h. The second stage heating temperature is 1050℃ and the heating and holding time is 7.5h. The third stage heating temperature is 1200℃ and the heating and holding time is 15h. The heated billet is transferred to a mechanical descaling machine for descaling, then briefly reheated to 1200℃ for 45 minutes. Before the billet is extruded, the extrusion cylinder, extrusion die, and mandrel are preheated to 500℃, and graphite emulsion is applied to the die surface. After exiting the furnace, glass lubricant powder is sprayed onto the inner and outer surfaces of the billet. Finally, the reheated billet is transferred to a 50,000-ton extrusion press for direct extrusion and cavitation expansion. After extrusion, it is air-cooled to room temperature and then demolded. The transfer time after the billet exits the furnace is approximately 210 seconds; the extrusion pressure is 406MN, and the extrusion speed is 40mm / s. The specifications of the black tube after extrusion are: outer diameter Φ1295mm × inner diameter Φ1150mm. G115 steel black-skinned pipes are transferred to a bogie hearth furnace for stress-relief annealing. The black-skinned pipe billets are cold-charged into the furnace and heated in two stages. The first stage heating temperature is 400℃, and the heating and holding time is 8.5h. The second stage heating temperature is 780℃, and the heating and holding time is 11h. After the holding time is completed, the billets are cooled to 400℃ in the furnace and then quickly transferred to a horizontal pressure straightening machine for three-point pressure straightening. After multiple passes of straightening, the curvature is 3mm / m. 4) Conditioning and tempering Quenching treatment, austenitizing temperature 1030℃, holding time 3h, water cooling; Tempering treatment, tempering temperature 750℃, tempering time 5h, air cooling; 5) Finishing The inner and outer surfaces of the black-skinned pipes cooled to room temperature are machined or polished to a bright finish, with specifications of outer diameter Φ1280mm × wall thickness 60mm. 6) Tissue performance testing After finishing, the bright tubes were subjected to physical and chemical tests at designated locations according to technical requirements and standards, including macro- and micro-structures and mechanical properties. The test results are shown in Tables 5 and 6.

[0044] As shown in Table 5, this invention can obtain G115 steel pipes with high purity, and the inclusion levels of types A, B, C, D, and DS all meet the standard requirements. As shown in Table 6, the pipes prepared by the method of this invention have better performance than the standard requirements in all aspects, with the impact energy far exceeding the standard requirements, reaching over 150J.

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

Claims

1. A highly efficient, short-process method for preparing ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above, characterized in that, Includes the following steps: 1) Billet preparation Electroslag round ingots are obtained by electric furnace steelmaking followed by electroslag remelting, with a diameter ≥ Φ900mm and a length of 1500~3000mm. 2) Reverse extrusion perforation A three-stage heating and holding method is adopted. The first stage heating temperature is 600~850℃, and the heating and holding time is 5~8 hours. The second stage heating temperature is 1000~1100℃, and the heating and holding time is 7~11 hours. The third stage heating temperature is 1180~1280℃, and the heating and holding time is 13~20 hours. The heating rate is ≤150℃ / min, and the heating rate gradually decreases as the heating temperature increases. The total heating time is ≥25 hours. Then, it is subjected to reverse extrusion piercing in a vertical extrusion press with an extrusion pressure of 270~325MN and a reverse extrusion speed of 10~50mm / s. The specifications of the tube blank after reverse extrusion are outer diameter Φ1200~Φ1800mm × inner diameter Φ300~Φ500mm. After extrusion, it is slowly cooled to room temperature and then demolded. 3) Positive extrusion reaming A three-stage heating process is adopted: the first stage heating temperature is 500~750℃, and the heating and holding time is 5~9 hours; the second stage heating temperature is 1000~1100℃, and the heating and holding time is 7~11 hours; the third stage heating temperature is 1180~1280℃, and the heating and holding time is 13~20 hours. The billet is then subjected to positive extrusion in an extruder with an extrusion pressure of 375~425MN and a positive extrusion speed of 5~50mm / s. After positive extrusion, the specifications of the G115 steel pipe are an outer diameter of Φ1200~1800mm × a wall thickness of 40~250mm. After extrusion, the pipe is air-cooled to room temperature. The extruded G115 steel pipes are subjected to stress-relief annealing using a two-stage heating process. The first stage heating temperature is 400~600℃, and the heating and holding time is 4~9h. The second stage heating temperature is 750~800℃, and the heating and holding time is 11~14h. After annealing, the pipes are cooled in the furnace to 350~500℃ before being removed from the furnace. 4) Tempering heat treatment Quenching treatment, normalizing temperature 1030~1100℃, holding time 2~7h, water cooling; Tempering treatment, tempering temperature 750~800℃, tempering time 4~10h, air cooling.

2. The efficient short-process preparation method for ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above as described in claim 1, characterized in that, Step 2) Load the furnace using a cold furnace or a furnace temperature ≤500℃.

3. The efficient short-process preparation method for ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above as described in claim 1 or 2, characterized in that, Step 2) Transfer the heated billet to a mechanical descaling machine to remove the oxide scale. After descaling, return it to the furnace for a short time to reheat to 1180~1280℃ for 20~50 minutes.

4. The efficient short-process preparation method for ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above as described in claim 1, characterized in that, Step 3) Load the furnace using a cold furnace or a furnace temperature ≤500℃.

5. The efficient short-process preparation method for ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above as described in claim 1 or 4, characterized in that, Step 3) Transfer the heated billet to a mechanical descaling machine to remove the oxide scale. After descaling, return it to the furnace for a short period of reheating to 1180~1280℃ for 20~50 minutes.

6. The efficient short-process preparation method for ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above, as described in claim 1, 4, or 5, is characterized in that... Step 3) Before the tube blank is extruded, the extrusion cylinder, extrusion die and mandrel are preheated to a temperature of ≤500℃. At the same time, graphite emulsion is applied to the surface of the die to reduce friction. After the tube blank is taken out of the furnace, glass lubricating powder is sprayed on the inner and outer surfaces.

7. The efficient short-process preparation method for ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above, as described in claim 1, 4, 5, or 6, is characterized in that... Step 3) Annealing is performed by loading the furnace into a cold furnace or by loading the furnace at a temperature ≤500℃.

8. The efficient short-process preparation method for ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above, as described in claim 1, 4, 5, or 7, is characterized in that... Step 3) After annealing and exiting the furnace, the furnace is transferred to a horizontal pressure straightening machine for three-point pressure straightening to ensure that the curvature is ≤3mm / m.

9. The efficient short-process preparation method for ultra-large diameter G115 heat-resistant steel seamless tubes with diameters of Φ1200mm and above as described in claim 1, characterized in that, Step 1) Before the electroslag round ingot is discharged from the furnace, preheat the billet cylinder and mandrel to ≤500℃, and spray graphite emulsion inside the billet cylinder and on the surface of the mandrel. After the electroslag round ingot is discharged from the furnace, spray glass lubricating powder on the upper surface and the outer circumference.

Images