G115 large-specification continuous casting round billet forging method

Abstract

A forging method for a G115 large-size continuous casting round billet comprises the following steps that (1) high-temperature homogenization treatment is conducted, specifically, the G115 large-size continuous casting round billet is heated to 600-650 DEG C at the speed of 50-80 DEG C / h, heat preservation is conducted for 5-8 h, the G115 large-size continuous casting round billet continues to be heated to 1000-1050 DEG C at the speed of 50-80 DEG C / h, heat preservation is conducted for 3-5 h, then the G115 large-size continuous casting round billet continues to be heated to 1240-1280 DEG C at the speed of 50-80 DEG C / h, heat preservation is conducted for 30-50 h, heating is stopped, the furnace temperature is reduced to 800-1000 DEG C, and then the G115 large-size continuous casting round billet is heated to the forging heating temperature; the method comprises the following steps of (1) preparing a continuous casting round billet, (2) forging and heating: heating the continuous casting round billet to 1160-1200 DEG C at the speed of 50-100 DEG C / h and keeping the temperature for 5-10 hours, (3) forging: forging the continuous casting round billet on a high-speed forging machine at the initial forging temperature of 1100-1150 DEG C and the final forging temperature of 850-900 DEG C to obtain a forged piece, (4) annealing heat treatment, and (5) quenching and tempering heat treatment.

Description

Technical Field

[0001] This invention relates to the field of heat-resistant steel technology, specifically to a method for forging large-size continuous casting round billets of G115 steel. Background Technology

[0002] With rapid economic development, the demand for energy is increasing. Thermal power generation is an important component of my country's energy mix. However, the environmental pollution problems caused by thermal power generation are increasingly conflicting with my country's ecological civilization construction and environmental protection concepts. Therefore, the demand for high-efficiency, low-emission, high-parameter thermal power units is becoming increasingly urgent. The higher the steam temperature and pressure parameters of coal-fired power generation, the lower the coal consumption and the less pollutant emissions, but the higher the performance requirements for materials. The P92 material used in ultra-supercritical units with a high-temperature resistance of 600℃ is no longer sufficient to meet the requirements of higher-parameter units; and to build ultra-supercritical units with parameters above 630℃, the high-temperature resistance of materials must reach 650℃.

[0003] G115 is a martensitic heat-resistant steel, as disclosed in Chinese patent CN103045962B. This heat-resistant steel adopts the principle of composite strengthening and contains multiple strengthening elements such as W, Co, Cu, B, and N. Its high-temperature long-term aging stability, high-temperature creep strength, and oxidation resistance are significantly higher than P92. It is suitable for long-term use under high-pressure conditions at temperatures below 650℃. Comparative studies have found that G115 has better creep strength and oxidation resistance at 650℃ than P92 at 600℃.

[0004] The traditional manufacturing process for G115 martensitic heat-resistant steel involves ingot casting + (electroslag) + forging + tube making. However, the existing ingot casting + (electroslag) + forging process is costly, has a long production cycle, is complex, and there is still room for improvement in its microstructure and properties.

[0005] In the prior art, Chinese patent CN103045962B is an invention patent for G115, which mainly involves the composition design, strengthening concept, manufacturing method and performance characteristics of G115, but does not involve the forging method of G115.

[0006] Chinese patent CN108998650A relates to a method for manufacturing G115 large-diameter thick-walled seamless steel pipes for 630℃ ultra-supercritical units. This patent only relates to the pipe-making process of G115 large-diameter thick-walled seamless steel pipes and does not include the forging process.

[0007] Chinese patent CN108950148A relates to a method for improving the radial microstructure and property uniformity of G115 large-diameter thick-walled tubes, but this technology does not involve the forging method of G115.

[0008] Chinese patent CN114635023A relates to a method for producing martensitic heat-resistant steel billets, primarily involving the forging process of G115 electroslag ingots. The high-temperature homogenization temperature is 1200~1250℃, requiring a holding time of ≥80 hours, which is time-consuming and inefficient. The forging heating temperature is 1140~1180℃, and the upsetting and drawing processes cannot be completed in a single pass, requiring six passes (three upsetting and three drawing processes). This results in a long production cycle and low efficiency. Furthermore, this patent does not cover the forging of G115 continuously cast billets. Therefore, there is an urgent need to develop a new, efficient forging process suitable for G115 steel continuously cast large round billets, improving performance and quality while increasing production efficiency and reducing costs. Summary of the Invention

[0009] The purpose of this invention is to provide a method for forging large-size continuous casting round billets of G115 steel, which can significantly shorten the forging production cycle of G115 forgings, increase production efficiency by 30%, reduce costs by 45%, and improve microstructure and properties. The produced G115 forgings meet the performance requirements of "CSTM 00017.3-2021 Martensitic Heat-Resistant Steel 08Cr9W3Co3VNbCuBN (G115) for Power Plants - Part 3: Forgings", "Q / OAPD 2753-2022 New Martensitic Heat-Resistant Steel 08Cr9W3Co3VNbCuBN (G115) for Power Plants - Tube Billets and Profiles" and other standards. Steel pipes produced using these forgings as billets meet the performance requirements of "Q / OAPD 2253-2022 New Martensitic Heat-Resistant Steel 08Cr9W3Co3VNbCuBN (G115) for Power Plants - Seamless Steel Pipes" and "CSTM..." Requirements of "00017-2021 Seamless Steel Pipe of Martensitic Heat-Resistant Steel 08Cr9W3Co3VNbCuBN (G115) for Power Plants".

[0010] To achieve the above objectives, the technical solution of the present invention is as follows: This invention employs a process of continuous casting of large-sized round billets, high-temperature homogenization, and forging. Through comprehensive optimization of the high-temperature homogenization temperature, forging heating temperature, forging deformation process parameters, annealing process, and tempering heat treatment process, the goal of breaking down the as-cast structure of the continuously cast billet, eliminating segregation, and refining the grains is achieved.

[0011] Specifically, the forging method for G115 large-size continuous casting round billets of the present invention includes the following steps: 1) High-temperature homogenization treatment The G115 large-size continuous casting round billet is heated to 600-650℃ at a rate of 50-80℃ / h and held for 5-8 hours. The temperature is then increased to 1000-1050℃ at a rate of 50-80℃ / h and held for 3-5 hours. The temperature is then increased to 1240-1280℃ at a rate of 50-80℃ / h and held for 30-50 hours. Heating is then stopped, and the furnace temperature is lowered to 800-1000℃ before being raised to the forging heating temperature. The G115 large-size continuous casting round billet has a diameter of φ600-1200mm and a weight of 10-17 tons. Preferably, an anti-oxidation coating is sprayed onto the surface of the continuous casting round billet before heating. 2) Forging heating The continuously cast round billet is heated to 1160-1200℃ at a rate of 50-100℃ / h and held for 5-10h. 3) Forging The continuously cast round billet is forged on a high-speed forging mill. The initial forging temperature is 1100~1150℃, and the final forging temperature is 850~900℃. The forging process involves at least three upsetting and three drawing operations to form the forging. The height of each upsetting reduction ΔH ≤ H0 / 2, where H0 is the original height before upsetting. The upsetting ratio is 2.3~2. The drawing ratio for the wide-anvil high-pressure forging method is 2.7~3.2. The deformation per anvil is 20~25%, and the forging reduction rate is 0.001s. -1 ~0.05s -1 The initial reduction should be controlled at 50-70mm each time, and then gradually increased to 100-120mm. During the forging process, when the surface temperature is below 900℃, the furnace should be reheated and held at 1160-1200℃ for ≥3 hours. When forging the final product, the forging temperature should be controlled at 850-950℃. 4) Annealing heat treatment The annealing temperature is 770~790℃, the annealing time is 15~30h, and after annealing, the furnace is cooled to below 200℃, and then the furnace is air-cooled to room temperature. 5) Quenching and tempering heat treatment The quenching and tempering heat treatment includes quenching and tempering. The quenching temperature is 1060~1080℃ and the water is used for cooling. The tempering temperature is 770~790℃ and the air is used for cooling.

[0012] Furthermore, the weight percentage composition of the G115 large-size continuous casting round billet is as follows: C 0.060~0.100%, Si≤0.55%, Mn 0.27~0.73%, P≤0.020%, S≤0.010%, Cr 8.40~9.60%, W 2.33~3.17%, Co 2.80~3.25%, Cu 0.40~1.20%, V 0.13~0.27%, Nb 0.03~0.10%, N 0.005~0.019%, B 0.008~0.022%, Ni≤0.13%, Ti≤0.02%, Al≤0.015%, O≤0.0040%, As≤0.015%, Sb≤0.015%, Bi≤0.005%, Sn≤0.020%, Pb≤0.015%, As+Sb+Bi+Sn+Pb≤0.035%, balance is Fe and unavoidable impurities.

[0013] Preferably, in step 3), the upper and lower anvils are preheated before forging begins, and the preheating temperature of the anvil surfaces is not lower than 500°C.

[0014] In step 4), annealing is performed within 2 hours after forging is completed.

[0015] Preferably, in step 5), the forging is subjected to quenching and tempering heat treatment by heating to 900-1000℃ at a rate of 50-80℃ / h, holding at that temperature for at least 2 hours, then continuing to heat to 1060-1080℃ at a rate of 50-80℃ / h for quenching, holding at that temperature for 5-10 hours, and then water-cooled to room temperature; then heating to 770-790℃ at a rate of 50-80℃ / h for tempering, holding at that temperature for 7-12 hours, and then air-cooled to room temperature.

[0016] In the G115 large-size continuous casting round billet forging method described in this invention: In step 1), during the high-temperature homogenization treatment, the continuously cast round billet is heated to 600-650℃ at a rate of 50-80℃ / h and held for 5-8h. Then, the temperature is increased to 1000-1050℃ at a rate of 50-80℃ / h and held for 3-5h. Finally, the temperature is increased to 1240-1280℃ at a rate of 50-80℃ / h and held for 30-50h. Heating is then stopped, and the furnace temperature is lowered to 800-1000℃ before being raised to the forging heating temperature.

[0017] Compared with the original technology, the temperature of high-temperature homogenization has been significantly increased (from 1200~1250℃ to 1240~1280℃), the time of high-temperature homogenization has been shortened (from ≥80h to 30~50h), the production efficiency of high-temperature homogenization has been increased by 50%, and the cost has been reduced by 45%.

[0018] According to the Arrhenius formula, D = D0 * exp(-Q / RT) (where D0 is 1.7 × 10⁻⁶). -4 m 2 The diffusion coefficient of tungsten in G115 steel at 1200℃ is calculated to be 2.30 × 10⁻⁶ / s (Q = 311 kJ / mol). -15 m 2 / s, at 1250℃ is 6.84×10 -15 m 2 / s, at 1280℃ is 1.24×10 -14 m 2 / s, it can be seen that the diffusion coefficient of tungsten in G115 steel at 1280℃ is 5.4 times that at 1200℃. Combining the calculated phase diagram and the results of high-temperature confocal metallographic test, the high-temperature homogenization temperature is increased to 1240~1280℃. Under the premise of ensuring that overheating and burning do not occur, the efficiency of high-temperature diffusion can be significantly improved, the holding time of high-temperature homogenization can be shortened by 50%, and the cost can be reduced by 45%.

[0019] In particular, this invention employs a stepped heating method, which can significantly reduce thermal stress. The temperature is increased to 600-650℃ at a rate of 50-80℃ / h, reaching the first temperature range with the largest temperature difference between the surface and the core. At this point, the core temperature is below 300℃, making it prone to internal cracking due to stress caused by the large temperature difference. Holding this temperature for 5-8 hours ensures uniform temperature between the surface and the core, effectively reducing thermal stress. The temperature is then increased to 1000-1050℃ at a rate of 50-80℃ / h, reaching the second temperature range with the largest temperature difference, where the core temperature is below 750℃. Holding this temperature for 3-5 hours reduces the temperature difference between the surface and the core, preventing excessive positive thermal stress from causing cracks. Finally, the temperature is increased to 1240-1280℃ at a rate of 50-80℃ / h. This temperature range allows for maximum atomic diffusion efficiency, increasing diffusion efficiency by 5 times compared to the original process. This effectively eliminates component segregation while avoiding overheating. Holding this temperature for 30-50 hours achieves good homogenization.

[0020] In step 2), the forging heating is carried out at a rate of 50~100℃ / h to 1160~1200℃, with a holding time of 5~10h. Based on the thermal simulation tensile and compression tests, combined with the analysis of the hot working diagram, the deformation temperature of G115 is increased from the original 1140~1180℃ to 1160~1200℃. This can improve production efficiency, completing upsetting and drawing in one pass, reducing the total number of passes from the original 6 to 3, significantly improving production efficiency and reducing costs.

[0021] It should be noted that rapidly heating to 1160-1200℃ at a rate of 50-100℃ / h can shorten the heating time, inhibit grain growth at high temperatures, and at the same time improve production efficiency and reduce energy consumption.

[0022] In step 3), the initial forging temperature is 1100~1150℃, and the final forging temperature is 850~900℃. The initial forging temperature of 1100~1150℃ avoids boron segregation at grain boundaries, which can cause stress cracking during deformation, reducing the risk of forging cracks in high-boron G115 martensitic heat-resistant steel, and also preventing excessive grain growth. The final forging temperature of 850~900℃ ensures sufficient recrystallization, uniform grains, good deformation plasticity, and prevents cracking.

[0023] In step 3), the upper and lower anvils are preheated before forging begins, with the anvil surface preheating temperature not lower than 500℃. If the blank is fed directly onto a cold anvil for forging, the local temperature of the blank may drop suddenly, resulting in a significant decrease in plasticity and surface cracking during deformation.

[0024] In step 3), the forging process includes at least three upsetting steps and three drawing steps (the number of upsetting and drawing steps can be increased, but not less than three) to ensure that the center of the billet is deformed in place and the structure is uniform.

[0025] The height ΔH of each upsetting reduction is ≤ H0 / 2, where H0 is the original height before upsetting. The drawing process employs a wide-anvil high-pressure forging method to ensure proper deformation at the billet center and uniform microstructure. The upsetting ratio is 2.3~2.7, and the forging ratio for the wide-anvil high-pressure forging method is 2.7~3.2. The deformation per anvil is 20~25%, and the forging reduction rate is 0.001s. -1 ~0.05s -1 Initially, the compression amount should be controlled at 50-70mm each time, and then gradually increased to 100-120mm.

[0026] Employing a three-upsetting and three-drawing, wide-anvil high-pressure forging method ensures a total forging ratio ≥6, especially guaranteeing deformation of the central region where segregation and defects are most severe in the billet. This process also addresses internal casting defects (central shrinkage cavities, porosity), breaks up the as-cast structure, refines grains, eliminates segregation, and improves the uniformity of the forging's microstructure. G115 has a high alloy content and exhibits severe segregation in its as-cast structure. Large segregated phases significantly affect the mechanical and weldability of G115. Therefore, thorough breaking up of the as-cast structure and elimination of segregation are necessary to ensure that G115 forgings meet performance standards.

[0027] In addition, since the actual boron content of G115 is 0.012~0.018%, when the deformation rate is too high, boron rapidly diffuses to the grain boundaries, causing non-equilibrium segregation at the grain boundaries, which leads to a decrease in the plasticity of the steel. When the deformation rate is too low, the grains after dynamic recrystallization have enough time to grow, and the grains become coarser, which also leads to a decrease in plasticity and increases the risk of forging cracks.

[0028] In step 3), during the forging process, when the surface temperature of the billet is below 900℃, it is reheated in the furnace and held at 1160~1200℃ for ≥3 hours. In step 3), the temperature of the final forging deformation is limited. Forging is carried out at medium and low temperatures. Combined with appropriate deformation rate and deformation amount, sufficient recrystallization can be ensured, which helps to control grain growth and ensure the uniformity of internal and external grains. The final forging deformation temperature is 850~950℃, and the grain size is controlled at a uniform level of 2.0~4.0.

[0029] In step 4), the forging is annealed, preferably within 2 hours of forging completion. The annealing temperature is controlled at 780±10℃ (this temperature is the actual steel temperature, and should not exceed Ac1 of G115, i.e., ≤800℃, to prevent ineffective annealing and cracking. If the actual heating temperature exceeds Ac1, the local structure of G115, especially the original austenite grain boundaries and carbon-rich areas, will transform into austenite. However, this temperature slightly above 800℃ is not enough to make the austenitization complete and uniform. During the subsequent furnace cooling or air cooling process, these non-uniform and incompletely austenitized areas will re-transform into martensite. These newly formed high-carbon, high-hardness martensite will generate huge phase transformation stress. In addition, the newly formed untempered martensite is very brittle. With the superposition of huge stress, brittle cracking is very likely to occur). The annealing time is 15~30 hours. After annealing, the forging is cooled to below 200℃ in the furnace and then air-cooled to room temperature.

[0030] It should be noted that 780±10℃ is the actual steel temperature, not the temperature displayed on the furnace instrument. The actual billet temperature during heating should not exceed Ac1 of G115, which is ≤800℃, to prevent ineffective annealing and cracking.

[0031] Preferably, in step 4), annealing is performed within 2 hours after forging is completed.

[0032] In step 5), the forging undergoes quenching and tempering heat treatment. The temperature is increased to 900-1000℃ at a rate of 50-80℃ / h, held for at least 2 hours, and then increased to 1070±10℃ at a rate of 50-80℃ / h for quenching. The quenching holding time is 5-10 hours, followed by water cooling to room temperature. Then, the temperature is increased to 780±10℃ at a rate of 50-80℃ / h (this is the actual steel temperature, and should not exceed Ac1 of G115, i.e., ≤800℃, to prevent phase transformation and excessive hardness. This is because if the actual heating temperature exceeds Ac1, the local microstructure of G115, especially the original austenite grain boundaries and carbon-rich regions, will transform into austenite. However, this temperature slightly above 800℃ is insufficient to transform the austenite... If the austenitized phase is completely and uniformly integrated, these non-uniform, incompletely austenitized regions will re-transform into martensite during subsequent furnace cooling or air cooling. These newly formed martensites have very high hardness and, when mixed with normally tempered martensite with normal hardness, result in an overall hardness that is excessively high, exceeding standard requirements. This excessive hardness is extremely harmful. The non-uniform structure will lead to uneven mechanical properties such as strength, toughness, and plasticity, creating weak points. Furthermore, due to the enormous stress during the phase transformation of the newly formed martensite, stress cracks may occur at these weak points, or premature failure may occur during use. Therefore, the actual tempering holding temperature should be strictly controlled below Ac1. Tempering should be carried out for 7-12 hours, followed by air cooling to room temperature.

[0033] It should be noted that a quenching temperature of 1070±10℃ is sufficient for austenitization and can avoid excessive grain growth. The tempering temperature of 780±10℃ is the actual forging temperature, and it should not exceed the Ac1 of G115, which is ≤800℃, to prevent phase transformation and excessive hardness.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: Compared with the production method of martensitic heat-resistant steel billet disclosed in Chinese patent CN114635023A, the process flow of both adopts high-temperature homogenization + three upsetting and drawing forging + annealing + tempering heat treatment. However, the present invention has made significant optimizations to the high-temperature homogenization temperature, upsetting and drawing forging, annealing and tempering heat treatment process parameters, which greatly improves production efficiency, improves quality and reduces costs.

[0035] 1. The forging method described in this invention significantly increases the temperature of high-temperature homogenization (from 1200~1250℃ to 1240~1280℃), shortens the time of high-temperature homogenization (from ≥80h to 30~50h), increases the production efficiency of high-temperature homogenization by 50%, and reduces costs by 45%.

[0036] 2. The forging heating temperature has been increased from the original 1140~1180℃ to 1160~1200℃, which can improve production efficiency. Upsetting and drawing can be completed in one heat, and the total number of heats has been reduced from the original 6 to 3, which greatly improves production efficiency and reduces costs by 45%.

[0037] 3. Strict control is exercised over the upsetting and drawing deformation amounts, rates, and methods. A wide-anvil high-pressure forging method is used for drawing to ensure core deformation and the uniformity of the microstructure and properties of large-section forgings. The forging temperature for the final forging stage is limited to medium-low temperatures. Combined with appropriate deformation rates and amounts, this ensures sufficient recrystallization, helps control grain growth, and guarantees the uniformity of internal and external grains.

[0038] 4. Based on actual production experience and relevant tests, stricter limits have been imposed on annealing temperature, quenching temperature and tempering temperature to prevent problems such as cracking and excessive hardness. Attached Figure Description

[0039] Figure 1 This is a metallographic photograph showing the grain size of Example 1 of the present invention; Figure 2 Metallographic photographs showing the grain size of Example 2 of this invention; Figure 3 Metallographic photographs showing the grain size of Example 3 of the present invention; Figure 4 This is a metallographic photograph showing the grain size of Example 4 of the present invention; Figure 5 Metallographic photographs showing the grain size for comparison. Detailed Implementation

[0040] The present invention will be further described below with reference to the embodiments and accompanying drawings. Example 1

[0041] A method for forging large-size continuous casting round billets of G115 includes the following steps: 1) Use Φ1200 G115 continuous casting round billet, spray anti-oxidation coating evenly on the surface, load into the furnace and heat, raise the temperature to 600℃ at a rate of 50℃ / h, hold for 8h, continue to raise the temperature to 1000℃ at a rate of 50℃ / h, hold for 5h, continue to raise the temperature to 1280℃ at a rate of 50℃ / h, hold for 50h, stop heating, lower the furnace temperature to 800℃ and then raise the temperature to the forging heating temperature. 2) Heat to 1200℃ at a rate of 80℃ / h, hold for 10 hours, and then forge for the first time. 3) Before forging, the upper and lower anvils of the 8000-ton fast forging machine were preheated for 20 minutes with scrap steel at a temperature of 900℃. After the preheating was completed, the anvil surface temperature was measured to be 550℃. The first upsetting process involves upsetting the material to half its original height at a speed of 18 mm / s. The initial temperature at the start of upsetting is 1150℃. After upsetting, the material is drawn, with initial reductions controlled at 50 mm per stroke, gradually increasing to 100 mm. The resulting octagon is 1100 mm long and 2.2 m in length. The final forging temperature is 900℃. The material is then reheated in the furnace at 1200℃ for 6 hours. The second upsetting process uses the same process as the first upsetting process, upsetting to 1 / 2 of the original height, drawing it to 1100mm octagon, and the final forging temperature is 950℃; it is then reheated in the furnace and held at 1200℃ for 6 hours before being forged into the third upsetting process. The third forging process involves roughening the material to half its original height, drawing it to an octagonal shape of 1150mm, and then rounding it to a Φ1050 (-10mm, +20mm) forging. The final forging temperature is 950℃. 4) After forging, anneal in an annealing furnace for 1.5 hours at a temperature of 780℃ for 30 hours, then furnace-cooled to 200℃ and air-cooled after removal from the furnace; 5) Finally, perform quenching and tempering heat treatment. Heat the temperature to 900℃ at a rate of 50℃ / h, hold for 3 hours, then continue to heat the temperature to 1070℃ at a rate of 50℃ / h, hold for 10 hours, and then water cool to room temperature. Heat the temperature to 780℃ at a rate of 50℃ / h for tempering, hold for 12 hours, and then air cool to room temperature.

[0042] The low-magnification inspection results of the forgings are shown in Table 1. It can be seen that there is no central porosity or segregation, and the general porosity is only grade 0.5, which is far better than the standard requirement that the general porosity, central porosity, and ingot segregation should not exceed grade 2.0, and is also better than the comparative example.

[0043] The inclusions are shown in Table 2. The fine series of inclusions in category A is grade 0 and the coarse series is grade 0. The fine series of inclusions in category B is grade 0.5 and the coarse series is grade 0. The fine series of inclusions in category C is grade 0 and the coarse series is grade 0. The fine series of inclusions in category D is grade 1.0 and the coarse series is grade 0. The inclusions in category DS are grade 0. All of these are far better than the standard requirement of grade 1.0 to 2.5 and are also better than the comparative example.

[0044] Grain size is shown in Table 3, and metallographic photographs of grain size are shown in [reference needed]. Figure 1 The original austenite grain size is rated at 2.0~3.5, with a grade difference of 1.5, which is better than the original austenite grain size required by the steel pipe standard to be finer than grade 0, and also better than the comparative example. The grains are refined and uniform, and the microstructure is lath-shaped tempered martensite.

[0045] The mechanical properties are shown in Table 4. The yield strength and tensile strength are 25% and 14% higher than the standard requirements, respectively. The elongation is 47% higher than the standard requirements. The impact energy is 2.7 times higher than the standard requirements and is also better than the comparative example. The hardness value also meets the standard requirements of HBW195~250. It can be seen that the G115 forgings produced by the method of this invention have properties that are far superior to the standard requirements and also superior to the comparative example. Example 2

[0046] A method for forging large-size continuous casting round billets of G115 includes the following steps: 1) Use Φ1000 G115 continuous casting round billet, spray anti-oxidation coating evenly on the surface, load into the furnace and heat, raise the temperature to 620℃ at a rate of 60℃ / h, hold for 7h, continue to raise the temperature to 1020℃ at a rate of 60℃ / h, hold for 4h, continue to raise the temperature to 1280℃ at a rate of 60℃ / h, hold for 30h, stop heating, lower the furnace temperature to 900℃ and then raise the temperature to the forging heating temperature. 2) Heat to 1190℃ at a rate of 90℃ / h, hold for 8 hours, and then forge for the first time. 3) Before forging, the upper and lower anvils of the 8000-ton fast forging machine were preheated for 20 minutes with scrap steel at a temperature of 900℃. After the preheating was completed, the anvil surface temperature was measured to be 550℃. The first upsetting process involves upsetting to half the original height at a speed of 19 mm / s. The initial temperature at the start of upsetting is 1145℃. After upsetting, the drawing process begins, with initial reductions controlled at 60 mm per stroke, gradually increasing to 110 mm, resulting in an octagonal length of 900 mm and a final length of 2.2 m. The final forging temperature is 900℃. The furnace is then reheated at 1190℃ for 5 hours. The second upsetting process uses the same process as the first upsetting process, upsetting to 1 / 2 of the original height, drawing it to 900mm octagon, and finally forging at a temperature of 900℃; then it is reheated in the furnace and held at 1190℃ for 5 hours before being forged for the third time. The third forging process involves roughening the material to half its original height, drawing it to an octagonal shape of 1000mm, and then rounding it to a Φ900 (-10mm, +20mm) forging. The final forging temperature is 900℃. 4) After forging, anneal in an annealing furnace for 1.5 hours at a temperature of 770℃ for 25 hours, then furnace-cooled to 200℃ and air-cooled after removal from the furnace. 5) Finally, perform quenching and tempering heat treatment. Heat the temperature to 950℃ at a rate of 60℃ / h, hold for 2 hours, then continue to heat the temperature to 1060℃ at a rate of 60℃ / h, hold for 9 hours, and then water cool to room temperature. Heat the temperature to 770℃ at a rate of 80℃ / h for tempering, hold for 11 hours, and then air cool to room temperature.

[0047] The results of the low-magnification inspection of the forgings are shown in Table 1. It can be seen that there is no central porosity or segregation, and the general porosity is only grade 0.5, which is far better than the standard requirement that the general porosity, central porosity and ingot segregation should not be greater than grade 2.0, and is also better than the comparative example. The inclusions are shown in Table 2. The fine series of inclusions in category A is grade 0 and the coarse series is grade 0. The fine series of inclusions in category B is grade 0.5 and the coarse series is grade 0. The fine series of inclusions in category C is grade 0 and the coarse series is grade 0. The fine series of inclusions in category D is grade 1.0 and the coarse series is grade 0. The inclusions in category DS are grade 0. All of these are far better than the standard requirement of grade 1.0 to 2.5 and are also better than the comparative example.

[0048] Grain size is shown in Table 3, and metallographic photographs of grain size are shown in [reference needed]. Figure 2 The original austenite grain size is rated as 2.0~3.5, with a grade difference of 1.5, which is better than the original austenite grain size required by the steel pipe standard to be finer than grade 0, and also better than the comparative example; the grains are fine and uniform, and the microstructure is lath-shaped tempered martensite.

[0049] The mechanical properties are shown in Table 4. The yield strength and tensile strength are 26% and 14% higher than the standard requirements, respectively. The elongation is 49% higher than the standard requirements. The impact energy is 2.9 times higher than the standard requirements and is also better than the comparative example. The hardness value also meets the standard requirements of HBW195~250. It can be seen that the G115 forgings produced by this method have properties that are far superior to the standard requirements and also superior to the comparative example. Example 3

[0050] A method for forging large-size continuous casting round billets of G115 includes the following steps: 1) Use Φ800 G115 continuous casting round billet, spray anti-oxidation coating evenly on the surface, load into the furnace and heat, raise the temperature to 630℃ at a rate of 70℃ / h, hold for 6h, continue to raise the temperature to 1030℃ at a rate of 70℃ / h, hold for 4h, continue to raise the temperature to 1270℃ at a rate of 70℃ / h, hold for 40h, stop heating, lower the furnace temperature to 900℃ and then raise the temperature to the forging heating temperature. 2) Heat to 1180℃ at a rate of 90℃ / h, hold for 6 hours, and then forge for the first time. 3) Before forging, the upper and lower anvils of the 8000-ton fast forging machine were preheated for 20 minutes with scrap steel at a temperature of 900℃. After the preheating was completed, the anvil surface temperature was measured to be 550℃. The first upsetting process involves upsetting to half the original height at a speed of 20 mm / s. The initial temperature at the start of upsetting is 1140℃. After upsetting, the drawing process begins, with initial reductions controlled at 70 mm per stroke, gradually increasing to 120 mm, and finally drawing to an octagonal length of 800 mm, with a total length of 2.2 m. The final forging temperature is 870℃. The furnace is then reheated to a holding temperature of 1180℃ for 4 hours. The second upsetting process uses the same process as the first upsetting process, upsetting to 1 / 2 of the original height, drawing it to an octagonal length of 800mm, and finally forging at a temperature of 870℃; then it is reheated in the furnace and held at 1160℃ for 3 hours before being forged for the third time. The third forging process involves roughening the material to half its original height, drawing it to an octagonal shape of 800mm, and then rounding it to a Φ700 (-10mm, +20mm) forging. The final forging temperature is 870℃. 4) After forging, anneal in an annealing furnace for 1.5 hours at a temperature of 790℃ for 20 hours, then furnace-cooled to 200℃ and air-cooled after removal from the furnace. 5) Finally, perform quenching and tempering heat treatment. Heat the temperature to 950℃ at a rate of 70℃ / h, hold for 2 hours, then continue to heat the temperature to 1080℃ at a rate of 70℃ / h, hold for 7 hours, and then water cool to room temperature. Heat the temperature to 790℃ at a rate of 70℃ / h for tempering, hold for 9 hours, and then air cool to room temperature.

[0051] The low-magnification inspection results of the forgings are shown in Table 1. It can be seen that there is no central porosity or segregation, and the general porosity is only grade 0.5, which is far better than the standard requirement that the general porosity, central porosity, and ingot segregation should not exceed grade 2.0, and is also better than the comparative example.

[0052] The inclusions are shown in Table 2. The fine series of inclusions in category A is grade 0 and the coarse series is grade 0. The fine series of inclusions in category B is grade 0.5 and the coarse series is grade 0. The fine series of inclusions in category C is grade 0 and the coarse series is grade 0. The fine series of inclusions in category D is grade 1.0 and the coarse series is grade 0. The inclusions in category DS are grade 0. All of these are far better than the standard requirement of grade 1.0 to 2.5 and are also better than the comparative example.

[0053] Grain size is shown in Table 3, and metallographic photographs of grain size are shown in [reference needed]. Figure 3 The original austenite grain size is rated as 2.0~4.0, with a difference of 2 grades, which is better than the original austenite grain size required by the steel pipe standard to be finer than grade 0, and also better than the comparative example. The grains are refined and uniform, and the microstructure is lath-shaped tempered martensite.

[0054] The mechanical properties are shown in Table 4. The yield strength and tensile strength are 26% and 15% higher than the standard requirements, respectively. The elongation is 46% higher than the standard requirements. The impact energy is 2.8 times higher than the standard requirements and is also better than the comparative example. The hardness value also meets the standard requirements of HBW195~250. It can be seen that the G115 forgings produced by this method have properties that are far superior to the standard requirements and also superior to the comparative example. Example 4

[0055] A method for forging large-size continuous casting round billets of G115 includes the following steps: 1) Use Φ700 G115 continuous casting round billet, spray anti-oxidation coating evenly on the surface, load into the furnace and heat, raise the temperature to 650℃ at a rate of 80℃ / h, hold for 5h, continue to raise the temperature to 1050℃ at a rate of 80℃ / h, hold for 3h, continue to raise the temperature to 1240℃ at a rate of 80℃ / h, hold for 50h, stop heating, lower the furnace temperature to 800℃ and then raise the temperature to the forging heating temperature. 2) Heat to 1160℃ at a rate of 100℃ / h, hold for 5 hours, and then forge for the first time. 3) Before forging, the upper and lower anvils of the 8000-ton fast forging machine were preheated for 20 minutes with scrap steel at a temperature of 900℃. After the preheating was completed, the anvil surface temperature was measured to be 550℃. The first upsetting process involves upsetting to half the original height at a speed of 18-20 mm / s. The initial temperature at the start of upsetting is 1145℃. After upsetting, the drawing process begins, with initial reductions controlled at 50-70 mm per stroke, gradually increasing to 100-120 mm, resulting in an octagonal length of 700 mm and a final length of 2.1 m. The final forging temperature is 850℃. The furnace is then reheated to a holding temperature of 1160℃ for 3 hours. The second upsetting process uses the same process as the first upsetting process, upsetting to 1 / 2 of the original height, drawing it to a 700mm octagon, and the final forging temperature is 850℃; it is then reheated in the furnace and held at 1160℃ for 3 hours before being forged for the third time. The third forging process involves roughening the material to half its original height, drawing it to a 700mm octagonal shape, and then rounding it to a Φ650 (-10mm, +20mm) forging. The final forging temperature is 850℃. 4) After forging, anneal in an annealing furnace for 1.5 hours at a temperature of 780℃ for 15 hours, then furnace-cooled to 200℃ and air-cooled after removal from the furnace. 5) Tempering heat treatment: Heat to 1000℃ at a rate of 80℃ / h, hold for 2 hours, then continue to heat to 1070℃ at a rate of 80℃ / h, hold for 5 hours, and then water cool to room temperature; heat to 780℃ at a rate of 80℃ / h for tempering, hold for 7 hours, and then air cool to room temperature.

[0056] The results of the low-magnification inspection of the forgings are shown in Table 1. It can be seen that there is no central porosity or segregation, and the general porosity is only grade 0.5, which is far better than the standard requirement that the general porosity, central porosity and ingot segregation should not be greater than grade 2.0, and is also better than the comparative example.

[0057] The inclusions are shown in Table 2. The fine series of inclusions in category A is grade 0 and the coarse series is grade 0. The fine series of inclusions in category B is grade 0.5 and the coarse series is grade 0. The fine series of inclusions in category C is grade 0 and the coarse series is grade 0. The fine series of inclusions in category D is grade 1.0 and the coarse series is grade 0. The inclusions in category DS are grade 0. All of these are far better than the standard requirement of grade 1.0 to 2.5 and are also better than the comparative example. Grain size is shown in Table 3, and metallographic photographs of grain size are shown in [reference needed]. Figure 4 The original austenite grain size is rated as 2.0~4.0, with a grade difference of 2, which is better than the original austenite grain size required by the steel pipe standard to be finer than grade 0, and also better than the comparative example; the grains are refined and uniform, and the microstructure is lath-shaped tempered martensite.

[0058] The mechanical properties are shown in Table 4. The yield strength and tensile strength are 28% and 16% higher than the standard requirements, respectively. The elongation is 57% higher than the standard requirements. The impact energy is 3.3 times higher than the standard requirements and is also better than the comparative example. The hardness value also meets the standard requirements of HBW195~250. It can be seen that the G115 forgings produced by this method have properties that are far superior to the standard requirements and also superior to the comparative example. Comparative Example

[0059] The G115 forgings produced according to the method of Chinese Patent CN114635023A are shown in Table 1 for low magnification inspection results. It can be seen that there is no central porosity and point segregation, and the general porosity and ingot shape segregation are grade 0.5. The general porosity, central porosity and ingot shape segregation meet the standard requirements that are no greater than grade 2.0, but it is not as good as the effect of the present invention.

[0060] The inclusions are shown in Table 2. Inclusions of type A are grade 0 for both fine and coarse components; inclusions of type B are grade 0.5 for both fine and coarse components; inclusions of type C are grade 0 for both fine and coarse components; inclusions of type D are grade 1.5 for both fine and coarse components; and inclusions of type DS are grade 0. They meet the standard requirements of grade 1.0 to 2.5, but inclusions of type D are not as effective as those of the present invention.

[0061] Grain size is shown in Table 3, and metallographic photographs of grain size are shown in [reference needed]. Figure 5 The original austenite grain size is rated as 1.0~3.0, which meets the requirements of the steel pipe standard. The original austenite grain size is finer than grade 0, but coarser than grade 2.0~4.0 of the present invention. The mechanical properties are shown in Table 4, which meet the standard requirements, but are 5~19% lower than the mechanical properties of the present invention.

[0062] In summary, the forgings and steel pipes produced by continuous casting of martensitic heat-resistant steel G115 in this invention meet the chemical composition, microstructure, and properties of CSTM standards and enterprise standards such as "CSTM 00017-2021 Seamless steel pipes of martensitic heat-resistant steel 08Cr9W3Co3VNbCuBN (G115) for power plants", "Q / OAPD 2753-2022 Tube blanks and profiles of new martensitic heat-resistant steel 08Cr9W3Co3VNbCuBN (G115) for power plants" and "Q / OAPD 2253-2022 Seamless steel pipes of new martensitic heat-resistant steel 08Cr9W3Co3VNbCuBN (G115) for power plants".

[0063]

[0064]

[0065]

[0066]

Claims

1. A method for forging large-size continuous casting round billets of G115, characterized in that, Includes the following steps: 1) High-temperature homogenization treatment The G115 large-size continuous casting round billet is heated to 600-650℃ at a rate of 50-80℃ / h and held for 5-8 hours. The temperature is then increased to 1000-1050℃ at a rate of 50-80℃ / h and held for 3-5 hours. The temperature is then increased to 1240-1280℃ at a rate of 50-80℃ / h and held for 30-50 hours. Heating is then stopped, and the furnace temperature is lowered to 800-1000℃ before being raised to the forging heating temperature. The G115 large-size continuous casting round billet has a diameter of φ600-1200mm and a weight of 10-17 tons. Preferably, an anti-oxidation coating is sprayed onto the surface of the continuous casting round billet before heating. 2) Forging heating The continuously cast round billet is heated to 1160-1200℃ at a rate of 50-100℃ / h and held for 5-10h. 3) Forging The continuously cast round billet is forged on a high-speed forging mill. The initial forging temperature is 1100~1150℃, and the final forging temperature is 850~900℃. The forging process involves at least three upsetting and three drawing operations to form the forging. The height of each upsetting reduction ΔH ≤ H0 / 2, where H0 is the original height before upsetting. The upsetting ratio is 2.3~2. The drawing ratio for the wide-anvil high-pressure forging method is 2.7~3.

2. The deformation per anvil is 20~25%, and the forging reduction rate is 0.001s. -1 ~0.05s -1 The initial reduction should be controlled at 50-70mm each time, and then gradually increased to 100-120mm. During the forging process, when the surface temperature is below 900℃, the furnace should be reheated and held at 1160-1200℃ for ≥3 hours. When forging the final product, the forging temperature should be controlled at 850-950℃. 4) Annealing heat treatment The annealing temperature is 770~790℃, the annealing time is 15~30h, and after annealing, the furnace is cooled to below 200℃, and then the furnace is air-cooled to room temperature. 5) Quenching and tempering heat treatment The quenching and tempering heat treatment includes quenching and tempering. The quenching temperature is 1060~1080℃ and the water is used for cooling. The tempering temperature is 770~790℃ and the air is used for cooling.

2. The forging method for large-size continuous casting round billets of G115 as described in claim 1, characterized in that, In step 3), the upper and lower anvils are preheated before forging begins, and the preheating temperature of the anvil surfaces is not lower than 500℃.

3. The forging method for G115 large-size continuous casting round billets as described in claim 1, characterized in that, In step 4), annealing is performed within 2 hours after forging is completed.

4. The forging method for large-size continuous casting round billets of G115 as described in claim 1, characterized in that, In step 5), the forging is subjected to quenching and tempering heat treatment. The temperature is raised to 900-1000℃ at a rate of 50-80℃ / h, held for at least 2 hours, and then raised to 1060-1080℃ at a rate of 50-80℃ / h for quenching. The quenching holding time is 5-10 hours, and the forging is water-cooled to room temperature. Then, the temperature is raised to 770-790℃ at a rate of 50-80℃ / h for tempering. The tempering holding time is 7-12 hours, and the forging is air-cooled to room temperature.

5. The forging method for large-size continuous casting round billets of G115 as described in claim 1, characterized in that, The composition by weight percentage of the G115 large-size continuously cast round billet is as follows: C 0.060~0.100%, Si≤0.55%, Mn 0.27~0.73%, P≤0.020%, S≤0.010%, Cr 8.40~9.60%, W 2.33~3.17%, Co 2.80~3.25%, Cu 0.40~1.20%, V 0.13~0.27%, Nb 0.03~0.10%, N 0.005~0.019%, B 0.008~0.022%, Ni≤0.13%, Ti≤0.02%, Al≤0.015%, O≤0.0040%, As≤0.015%, Sb≤0.015%, Bi≤0.005%, Sn≤0.020%, Pb≤0.015%, As+Sb+Bi+Sn+Pb≤0.035%, balance is Fe and unavoidable impurities.

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