A method for producing a 20-ton class large single weight G115 pipe blank

Abstract

The application discloses a production method of 20-ton large single-weight G115 pipe blank, which comprises the following steps: 1) the electric slag remelting melting speed is 14-18.5 kg / min, the electric slag top sealing melting speed is 9-13.5 kg / min, and the inert gas flow is 200-500 L / min; 2) the first stage homogenization temperature is 1240-1280 DEG C, the first stage homogenization time is 50-80 hours; the second stage homogenization temperature is 1140-1180 DEG C, and the second stage homogenization time is 5-8 hours; 3) the upsetting and drawing frequency is greater than or equal to 3 times, the upsetting is to 1 / 3-1 / 2 of the original height, and the height-diameter ratio after drawing is 1.8-2.4. Through the low melting speed electric slag remelting, the super-high temperature homogenization and the multiple times of forging, the composition uniformity and the comprehensive mechanical property of the large ingot type pipe blank are successfully improved to the level of the small ingot type, the harsh requirements of a 630 DEG C ultra-supercritical power station on the large-diameter thick-wall pipe are met, and a reliable mother material solution is provided for the large-scale and high-efficiency design of key components of the power station.

Description

Technical Field

[0001] This invention belongs to the field of heat-resistant steel production technology, specifically relating to a method for producing a 20-ton-class large single-weight G115 tube blank. Background Technology

[0002] G115 steel is a new type of martensitic heat-resistant steel independently developed in China, designed to solve the material bottleneck of high-temperature components in efficient and clean coal-fired power plants. Its characteristics include high strength, high toughness, excellent high-temperature oxidation resistance and corrosion resistance. At 650℃, its creep strength is 1.5 times that of P92 steel, allowing for thinner component walls and extended service life. It is mainly used in key pressure-bearing components of ultra-supercritical thermal power units, such as boiler headers and steam pipes, which can significantly improve power generation efficiency.

[0003] Applying it to power plant projects requires the production of 20-ton-class 1300-round G115 electroslag ingots. Since G115 steel is a medium-high alloy steel containing 9% chromium and 1% copper, the dispersed distribution of chromium and copper is beneficial for improving the material's oxidation resistance and mechanical properties. However, these two elements are prone to agglomeration, forming large-size chromium carbides and copper-rich phases, which not only reduce the material's strength but also significantly decrease its plasticity and toughness. Therefore, developing a complete production process for large-unit-weight G115 steel products is of great significance.

[0004] Chinese Patent Publication No. CN114635023A discloses a method for producing martensitic heat-resistant steel billets, describing a forging process for φ900~1200mm G115 electroslag ingots (10~15 tons), with a relatively low high-temperature homogenization temperature and a duration of ≥80 hours. This patent uses relatively small electroslag ingots and has a long finishing process.

[0005] Chinese Patent Publication No. CN121109762A discloses a production process for G115 electroslag ingots with a diameter of φ700-1000mm. This patent is based on a method for producing ultra-supercritical power plant martensitic heat-resistant steel G115 by electroslag remelting. The G115 electroslag ingots produced by this patent are relatively small in size. Summary of the Invention

[0006] The purpose of this invention is to provide a production method for 20-ton-class large single-weight G115 tube billets, significantly shortening the production time while avoiding ingot overheating, achieving homogenization of 20-ton-class φ1100~1300mm G115 steel, improving compositional segregation in large single-weight G115 tube billets, and ultimately producing large single-weight G115 finished tubes with properties consistent with those produced from small ingots, including room temperature tensile strength ≥660MPa, room temperature yield strength ≥480MPa, room temperature yield strength at 630℃ ≥271MPa, and room temperature impact strength AK. v2≥24J, meeting the actual requirements of a 630℃ ultra-supercritical power plant.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A method for producing a 20-ton-class large single-unit G115 tube billet specifically includes the following steps: 1) Electroslag remelting; The electroslag remelting melting rate is 14~18.5 kg / min, the electroslag capping melting rate is 9~13.5 kg / min, and inert gas protection is carried out during the electroslag remelting process with an inert gas flow rate of 200~500 L / min to obtain electroslag ingots. 2) Homogenization The surface of the electroslag ingot is coated with an anti-oxidation coating, and then subjected to a two-stage ultra-high temperature homogenization treatment. The first stage homogenization temperature is 1240~1280℃ and the first stage homogenization time is 50~80 hours; the second stage homogenization temperature is 1140~1180℃ and the second stage homogenization time is 5~8 hours. 3) Forging The upsetting and drawing process is ≥3 times. During each upsetting and drawing process, the billet is upset to 1 / 2 to 2 / 3 of its original height. The height-to-diameter ratio of the billet after drawing is 1.8 to 2.4.

[0008] Preferably, in step 1), the depth of the molten pool during the electroslag remelting process is 15~25mm.

[0009] Preferably, in step 1), the inert gas is argon.

[0010] The electroslag ingots of this invention have a size of φ1100~1300mm, which is in the 20-ton class.

[0011] The G115 heat-resistant steel of this invention has the following composition by weight percentage: 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: 0.03–0.1%. 0%, 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 impurity elements.

[0012] In the production method of 20-ton-class large single-weight G115 tube blank described in this invention: 1. Electroslag remelting (ESR) is the core process for refining G115 steel. The melting rate directly affects the stability of the molten pool and the degree of ingot segregation. G115 steel has a melting point of approximately 1450℃ and contains a high proportion of elements such as W and Cr. Its solidus and liquidus lines are relatively narrow (approximately 50℃). If the melting rate is too low (<14 kg / min), the molten pool will be too deep (>25 mm), leading to uneven heat conduction and dendritic segregation. If the melting rate is too high (>18.5 kg / min), the molten pool will fluctuate more significantly (molten pool depth <10 mm), causing splashing of molten metal droplets and the entrainment of inclusions. To maintain a molten pool depth of 15~25 mm, ensure sufficient heat diffusion, and allow elements such as Cr and W to achieve dynamic equilibrium at the solidification front, this invention sets the melting rate to 14~18.5 kg / min.

[0013] 2. The capping stage is a critical step in the final solidification period of the electroslag ingot. If the electroslag melting rate is too slow (<9 kg / min) during capping, the molten pool temperature will be too low, easily inducing thermal stress cracks, and the surface quality of the electroslag ingot will be poor, requiring additional peeling treatment, further reducing the yield of the electroslag ingot. If the electroslag melting rate is too fast (>13.5 kg / min) during capping, the molten pool temperature will be too high, the solidification time will be prolonged, resulting in the enrichment of W element in the central region of the head of the electroslag ingot, and uneven element distribution.

[0014] 3. Inert gas protection during electroslag remelting is a core measure to prevent oxidation in the ESR process. In this invention, the diameter of the electroslag ingot is 1100-1300 mm. The inert gas flow rate must cover the surface. If the inert gas flow rate is below 200 L / min, the gas protection effect is poor, leading to an increase in the oxygen, hydrogen, and nitrogen content in the steel, resulting in the loss of boron in G115 steel and causing the electroslag ingot to meet compositional requirements. If the inert gas flow rate is above 500 L / min, airflow disturbance causes instability in the molten pool, affecting the ingot density.

[0015] 4. Homogenization treatment adopts a two-stage ultra-high temperature homogenization treatment.

[0016] The first stage, ultra-high temperature homogenization, aims to eliminate coarse segregation. Parameter settings are based on diffusion theory and thermal stress control. According to the Arrhenius formula, D = D0 * exp(-Q / RT) (where D0 is 1.7 × 10⁻⁶). -4 m 2 Calculations based on Q (311 kJ / mol) show that the diffusion coefficient of tungsten in G115 at 1200 °C is 2.30 × 10⁻⁶. -15 m 2 / s, at 1250℃ is 6.84×10 -15 m 2 / s, which is 12.4×10 at 1280℃. -15 m2 The diffusion coefficient of tungsten in G115 at 1280℃ is 5.4 times that at 1200℃. To reduce energy consumption, the first-stage ultra-high temperature homogenization temperature is set at 1240~1280℃. If the temperature is below 1240℃, the homogenization time for G115 needs to be extended to 80 hours or more. If the temperature is above 1280℃, the segregated region in the center of the electroslag ingot is prone to transform into a pasty region, reducing the material's plasticity. If the holding time is less than 50 hours, the homogenization and diffusion effect in the central region of G115 is incomplete, and there may be problems with alloy element segregation and tungsten-based precipitate segregation later. If the holding time is more than 80 hours, the surface anti-oxidation coating effect is weakened, and the surface of the electroslag ingot cracks during subsequent forging, reducing the yield of G115, wasting energy, and increasing production costs. 20-ton-class electroslag ingots with a diameter of φ1100~1300mm require initial heat treatment at 1240~1280℃ for 50~80 hours. During this process, the surface iron content decreases significantly while the copper content relatively increases, exceeding the solubility of copper in iron. This leads to the formation of a network-like copper-rich phase at the grain boundaries, reducing the surface plasticity of the material and causing cracking during forging. Therefore, before homogenization treatment, the electroslag ingots of this invention require the application of an anti-oxidation coating to the surface to prevent a significant decrease in surface iron content.

[0017] After the first stage of ultra-high temperature homogenization treatment, the temperature needs to be lowered to the second stage of ultra-high temperature homogenization. If the heating temperature is below 1140℃, the hot working time is too short to complete upsetting and drawing in one pass. If the heating temperature is above 1180℃, the plasticity of G115 steel will be significantly reduced, making it prone to forging cracking. Therefore, the heating temperature is set at 1140~1180℃. To ensure the effect of hot working, the holding time needs to be set at 5~8 hours. If the holding time is less than 5 hours, the temperature in the central area of ​​the 1100~1300mm round G115 electroslag ingot will be higher than 1180℃, posing a risk of central cracking during hot working. If the holding time exceeds 8 hours, it will waste energy and increase production costs.

[0018] 5. Forging employs multiple forging processes. Multiple forging is key to refining grain size, improving mechanical properties, and reducing the dispersion of liquid precipitates. This invention relates to φ1100~1300mm G115 electroslag ingots. Through multiple upsetting and drawing processes, internal defects in the electroslag ingot are sealed, avoiding localized stress concentration caused by single forging and refining the original austenite grains. The height-to-diameter ratio during drawing is controlled between 1.8 and 2.4. If the height-to-diameter ratio is >2.4, double-bulge and side-bending problems may occur during upsetting of the electroslag ingot, reducing the upsetting effect. If the height-to-diameter ratio is <1.8, the electroslag ingot will be short and stout, and excessive stretching of the material in the middle of the outer ring of the electroslag ingot during upsetting will easily form microcracks.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention addresses the severe segregation of chromium and copper in large-weight (20-ton class) and large-diameter (φ1100~1300mm) G115 steel ingots, which easily leads to a sharp drop in toughness. Targeting the narrow solidification range of G115 steel, this invention precisely controls the electroslag remelting rate (14~18.5 kg / min) and the electroslag capping rate (9~13.5 kg / min) to stabilize the molten pool shape and suppress dendrite segregation at the solidification source. Combined with two-stage heating and multiple forging controls, this ensures uniform surface temperature of the large ingot core, effectively preventing internal defects. Furthermore, ultra-high temperature homogenization treatment (1240~1280℃, holding for 50~80 hours) improves production efficiency and reduces energy consumption and costs while maintaining homogenization effectiveness.

[0020] This invention systematically solves the problems of compositional segregation, microstructure inhomogeneity, and forging cracking in large single-weight G115 steel ingots through a synergistic process of "low-melting-rate electroslag remelting + ultra-high temperature homogenization + multiple forgings." It successfully improves the compositional uniformity and comprehensive mechanical properties of large ingot-shaped billets to a level comparable to that of small ingot products, achieving room temperature tensile strength ≥660MPa, room temperature yield strength ≥480MPa, room temperature yield strength at 630℃ ≥271MPa, and room temperature impact strength AK. v2 With a strength of ≥24J, it meets the stringent requirements of 630℃ ultra-supercritical power plants for large-diameter, thick-walled pipes, providing a reliable base material solution for the large-scale and high-efficiency design of key power plant components. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0022] Example 1 A method for producing a 20-ton-class large single-unit weight G115 tube billet includes the following steps: 1) Electroslag remelting The electroslag remelting melting rate is 15 kg / min, the electroslag capping melting rate is 10 kg / min, and argon gas protection is carried out during the electroslag remelting process with an argon gas flow rate of 300 L / min to obtain electroslag ingots. 2) Homogenization The surface of the electroslag ingot is coated with an anti-oxidation coating, and then subjected to a two-stage ultra-high temperature homogenization treatment. The first stage homogenization temperature is 1250~1270℃ and the first stage homogenization time is 65 hours; the second stage homogenization temperature is 1160~1180℃ and the second stage homogenization time is 5.5 hours. 3) Forging After three upsetting and drawing processes to the target specifications, the billet is upset to 1 / 2 of its original height, and the height-to-diameter ratio of the billet after drawing is 2.4. The obtained tube blank was processed using conventional technology to obtain a finished tube with dimensions of Φ1118mm×18mm (wall thickness).

[0023] The chemical composition of each region is shown in Table 1, and the mechanical properties are shown in Table 3. The large single-weight G115 tube blank obtained in Example 1 of this invention has relatively mild compositional segregation, with a room temperature tensile strength of 795 MPa, a room temperature yield strength of 655 MPa, a room temperature yield strength of 345 MPa at 630°C, and a room temperature impact strength of AK. v2 It is 88J.

[0024] Example 2 A method for producing a 20-ton-class large single-unit weight G115 tube billet includes the following steps: 1) Electroslag remelting The electroslag remelting melting rate is 14.5 kg / min, the electroslag capping melting rate is 9.5 kg / min, and argon gas protection is provided during the electroslag remelting process with an argon gas flow rate of 200 L / min to obtain electroslag ingots. 2) Homogenization The surface of the electroslag ingot is coated with an anti-oxidation coating, and then subjected to a two-stage ultra-high temperature homogenization treatment. The first stage homogenization temperature is 1260~1280℃ and the first stage homogenization time is 60 hours; the second stage homogenization temperature is 1160~1180℃ and the second stage homogenization time is 6 hours. 3) Forging After three upsetting and drawing processes to the target specifications, the billet is upset to 2 / 5 of its original height, and the height-to-diameter ratio of the billet after drawing is 2.2. The obtained tube blank was processed using conventional technology to obtain a finished tube with dimensions of Φ1118mm×18mm (wall thickness).

[0025] The chemical composition of each region is shown in Table 1, and the mechanical properties are shown in Table 3. The large single-weight G115 tube blank obtained in Example 2 of this invention has relatively mild compositional segregation, with a room temperature tensile strength of 810 MPa, a room temperature yield strength of 685 MPa, a room temperature yield strength of 380 MPa at 630°C, and a room temperature impact strength of AK. v2 It is 79J.

[0026] Example 3 A method for producing a 20-ton-class large single-unit weight G115 tube billet includes the following steps: 1) Electroslag remelting The electroslag remelting melting rate is 17.5 kg / min, the electroslag capping melting rate is 12.5 kg / min, and argon gas protection is provided during the electroslag remelting process with an argon gas flow rate of 500 L / min to obtain electroslag ingots; 2) Homogenization The surface of the electroslag ingot is coated with an anti-oxidation coating, and then subjected to a two-stage ultra-high temperature homogenization treatment. The first stage homogenization temperature is 1260~1280℃ and the first stage homogenization time is 70 hours; the second stage homogenization temperature is 1150~1160℃ and the second stage homogenization time is 5 hours. 3) Forging After three upsetting and drawing processes to the target specifications, the billet is upset to 1 / 2 of its original height, and the height-to-diameter ratio of the billet after drawing is 1.8. The obtained tube blank was processed using conventional technology to obtain a finished tube with dimensions of ID902mm×46mm (wall thickness).

[0027] The chemical composition of each region is shown in Table 1, and the mechanical properties are shown in Table 3. The large single-weight G115 tube blank obtained in Example 3 of this invention has relatively mild compositional segregation, with a room temperature tensile strength of 820 MPa, a room temperature yield strength of 700 MPa, a room temperature yield strength of 360 MPa at 630°C, and a room temperature impact strength of AK. v2 It is 81J.

[0028] Example 4 A method for producing a 20-ton-class large single-unit weight G115 tube billet includes the following steps: 1) Electroslag remelting The electroslag remelting melting rate is 18.5 kg / min, the electroslag capping melting rate is 13.5 kg / min, and argon gas protection is provided during the electroslag remelting process with an argon gas flow rate of 400 L / min to obtain electroslag ingots; 2) Homogenization The surface of the electroslag ingot is coated with an anti-oxidation coating, and then subjected to a two-stage ultra-high temperature homogenization treatment. The first stage homogenization temperature is 1240~1260℃ and the first stage homogenization time is 80 hours; the second stage homogenization temperature is 1140~1150℃ and the second stage homogenization time is 5 hours. 3) Forging After three upsetting and drawing processes to the target specifications, the billet is upset to 2 / 3 of its original height, and the height-to-diameter ratio of the billet after drawing is 2.0. The obtained tube blank was processed using conventional technology to obtain a finished tube with dimensions of ID902mm×46mm (wall thickness).

[0029] The chemical composition of each region is shown in Table 1, and the mechanical properties are shown in Table 3. The large single-weight G115 tube blank obtained in Example 4 of this invention has relatively mild compositional segregation, with a room temperature tensile strength of 820 MPa, a room temperature yield strength of 705 MPa, a room temperature yield strength of 365 MPa at 630°C, and a room temperature impact strength of AK. v2 It is 102J.

[0030] Comparative Example 1 A method for producing a 20-ton-class large single-unit weight G115 tube billet includes the following steps: 1) Electroslag remelting The electroslag remelting melting rate is 18 kg / min, the electroslag capping melting rate is 13 kg / min, and argon gas protection is provided during the electroslag remelting process with an argon gas flow rate of 400 L / min to obtain electroslag ingots. 2) Homogenization An anti-oxidation coating is applied to the surface of the electroslag ingot, followed by homogenization treatment. The first stage homogenization temperature is 1210~1230℃ and the first stage homogenization time is 80 hours; the second stage homogenization temperature is 1140~1150℃ and the second stage homogenization time is 6 hours. 3) Forging After three upsetting and drawing processes to the target specifications, the material is upset to 2 / 3 of its original height, and the height-to-diameter ratio of the material after drawing is 2.1. The obtained tube blank was processed using conventional technology to obtain a finished tube with dimensions of Φ1118mm×18mm (wall thickness).

[0031] The chemical composition of each region is shown in Table 1, and the mechanical properties are shown in Table 3.

[0032] In Comparative Example 1, the homogenization temperature in the first stage was relatively low, resulting in large single-weight G115 tube blanks with chromium and copper segregation, poor impact performance, a room temperature tensile strength of 670 MPa, a room temperature yield strength of 540 MPa, a room temperature yield strength of 295 MPa at 630℃, and a room temperature impact strength of AK. v2 22J, room temperature shock AK v2 The value is too low and does not meet the requirements of this invention.

[0033] Comparative Example 2 A method for producing a 20-ton-class large single-unit weight G115 tube billet includes the following steps: 1) Electroslag remelting The electroslag remelting melting rate is 21 kg / min, the electroslag capping melting rate is 15 kg / min, and argon gas protection is provided during the electroslag remelting process with an argon gas flow rate of 250 L / min to obtain electroslag ingots. 2) Homogenization An anti-oxidation coating is applied to the surface of the electroslag ingot, followed by a two-stage homogenization treatment. The first stage homogenization temperature is 1260~1280℃ and the first stage homogenization time is 60 hours. The second stage homogenization temperature is 1160~1180℃ and the second stage homogenization time is 6 hours. 3) Forging After three upsetting and drawing processes to the target specifications, the material is upset to half its original height, and the height-to-diameter ratio of the material after drawing is 2.3. The obtained tube blank was processed using conventional technology to obtain a finished tube with dimensions of ID902mm×46mm (wall thickness).

[0034] The chemical composition of each region is shown in Table 1, and the mechanical properties are shown in Table 3.

[0035] In Comparative Example 2, both the electroslag remelting rate and the electroslag capping rate were relatively high. The resulting large single-unit G115 billet exhibited chromium and copper segregation, poor impact performance, a room temperature tensile strength of 665 MPa, a room temperature yield strength of 515 MPa, a room temperature yield strength of 285 MPa at 630℃, and a room temperature impact strength of AK. v2 15J, room temperature shock AK v2 The value is too low and does not meet the requirements of this invention.

[0036] Comparative Example 3 The production method of G115 large-diameter tube blank includes the following steps: 1) Electroslag remelting The electroslag remelting melting rate is 10 kg / min, and the electroslag capping melting rate is 8 kg / min. Argon gas protection is applied during the electroslag remelting process, with an argon gas flow rate of 350 L / min, to obtain electroslag ingots; 2) Homogenization An anti-oxidation coating is applied to the surface of the electroslag ingot, followed by a two-stage homogenization treatment. The first stage homogenization temperature is 1260~1280℃ and the first stage homogenization time is 60 hours. The second stage homogenization temperature is 1160~1180℃ and the second stage homogenization time is 6 hours. 3) Forging During the first upsetting process, the electroslag ingot was upset to half its original height. During the drawing process, multiple cracks appeared on the surface of the ingot.

[0037] In Comparative Example 1, due to the large diameter of the crystallizer, the remelting rate was too low, and the electroslag melting rate was also low. Slag was drawn into the interior of the steel ingot, and after cooling, there were obvious slag grooves on the surface of the electroslag ingot. This caused multiple cracks to appear on the surface of the electroslag ingot during drawing, and the cracks extended into the interior of the electroslag ingot, making it impossible to continue upsetting. Production could not continue on site, and the electroslag ingot was scrapped.

[0038] Comparative Example 4 The production method of G115 large-diameter tube blank includes the following steps: 1) Electroslag remelting The electroslag remelting melting rate is 17 kg / min, the electroslag capping melting rate is 2 kg / min, and argon gas protection is provided during the electroslag remelting process with an argon gas flow rate of 400 L / min to obtain electroslag ingots.

[0039] 2) Homogenization The electroslag ingots undergo a two-stage homogenization process. The first stage homogenization temperature is 1260~1280℃ and the first stage homogenization time is 70 hours. The second stage homogenization temperature is 1160~1180℃ and the second stage homogenization time is 5.5 hours. 3) Forging During the first upsetting process, the electroslag ingot was upset to 2 / 5 of its original height. Multiple cracks appeared on the surface of the ingot during the drawing process.

[0040] In Comparative Example 4, the capping melting rate was too low and the surface of the electroslag ingot was not coated with an anti-oxidation coating, which caused surface cracking during the forging process. The cracks extended into the interior of the electroslag ingot, making it impossible to continue upsetting. The material was rolled into a round shape on site and then annealed in the furnace. After annealing, the surface cracks were removed by machining and the material was reheated and put into production.

[0041] Comparative Example 5 The production method of G115 large-diameter tube blank includes the following steps: 1) Electroslag remelting; The electroslag remelting melting rate is 15.5 kg / min, the electroslag capping melting rate is 11.5 kg / min, and argon gas protection is provided during the electroslag remelting process with an argon gas flow rate of 300 L / min to obtain electroslag ingots. 2) Homogenization An anti-oxidation coating is applied to the surface of the electroslag ingot, followed by a two-stage homogenization treatment. The first stage homogenization temperature is 1240~1260℃ and the first stage homogenization time is 75 hours. The second stage homogenization temperature is 1140~1160℃ and the second stage homogenization time is 8 hours. 3) Forging The first upsetting process reached 2 / 3 of the original height. After drawing, the height-to-diameter ratio of the electroslag ingot was 2.7. The second and third upsetting processes both exhibited a double-drum shape. The third upsetting process resulted in a side bend. After drawing, the deformation on the other side of the side bend was larger, and small cracks appeared on the surface. After forging and cooling, targeted spot grinding was performed.

[0042] The obtained tube blank was processed using conventional technology to obtain a finished tube with dimensions of ID520mm×120mm (wall thickness).

[0043] The chemical composition of each region is shown in Table 1, and the mechanical properties are shown in Table 3.

[0044] In Comparative Example 5, the forging aspect ratio was too high. Although the compositional segregation of the obtained large single-weight G115 tube blank was relatively mild, its properties were consistent with those of the G115 tube produced from the small ingot. The room temperature tensile strength was 795 MPa, the room temperature yield strength was 710 MPa, the room temperature yield strength at 630℃ was 360 MPa, and the room temperature impact strength (AK) was... v2The J value is 77J, which meets the performance requirements. However, a flaw was found in the middle section of the single tube blank. Upon dissection and analysis, an unclosed hole was found at the flaw location.

[0045] As can be clearly seen from Tables 1 and 3, the 20-ton G115 tube blank prepared using the method described in this invention exhibits less compositional segregation, resulting in better impact performance of the finished tube. However, the large single-unit G115 tube blank produced according to Comparative Example 1 shows chromium and copper segregation, leading to poorer impact performance of the finished tube.

[0046] In summary, this invention reduces the segregation tendency of G115 electroslag ingots through low-melting-rate smelting, and improves the compositional uniformity of the billet through low-melting-rate remelting + ultra-high temperature homogenization + forging. Ultimately, the properties of the large-unit-weight G115 finished tubes are consistent with those of G115 tubes produced from small ingots: room temperature tensile strength ≥660MPa, room temperature yield strength ≥480MPa, room temperature yield strength at 630℃ ≥271MPa, and room temperature impact strength AK... v2 ≥24J, meeting the actual needs of the Datang Yuncheng Power Station project.

[0047]

[0048] Note: R is the radius.

[0049]

[0050]

Claims

1. A method for producing a 20-ton-class large single-unit weight G115 tube billet, characterized in that, Includes the following steps: 1) Electroslag remelting The electroslag remelting melting rate is 14~18.5 kg / min, the electroslag capping melting rate is 9~13.5 kg / min, and inert gas protection is carried out during the electroslag remelting process with an inert gas flow rate of 200~500 L / min to obtain electroslag ingots. 2) Homogenization The surface of the electroslag ingot is coated with an anti-oxidation coating, and then subjected to a two-stage ultra-high temperature homogenization treatment. The first stage homogenization temperature is 1240~1280℃ and the first stage homogenization time is 50~80 hours; the second stage homogenization temperature is 1140~1180℃ and the second stage homogenization time is 5~8 hours. 3) Forging The upsetting and drawing process is ≥3 times. During each upsetting and drawing process, the billet is upset to 1 / 2 to 2 / 3 of its original height. The height-to-diameter ratio of the billet after drawing is 1.8 to 2.

4.

2. The production method of 20-ton class large single-unit weight G115 tube blank as described in claim 1, characterized in that, In step 1), the depth of the molten pool during the electroslag remelting process is 15~25mm.

3. The production method of 20-ton class large single-unit weight G115 tube blank as described in claim 1 or 2, characterized in that, In step 1), the inert gas is argon.

4. The production method of 20-ton class large single-unit weight G115 tube blank as described in claim 1, characterized in that, The electroslag ingots are 20-ton grade, φ1100~1300mm in size.

5. The method for producing 20-ton class large single-unit weight G115 tube blanks as described in claim 1, characterized in that, The weight percentage composition of the G115 heat-resistant steel 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%, with the balance being Fe and unavoidable impurity elements.

6. The method for producing 20-ton class large single-unit weight G115 tube blanks as described in claim 1, characterized in that, The G115 tube blank should have a room temperature tensile strength ≥660MPa, a room temperature yield strength ≥480MPa, a room temperature yield strength at 630℃ ≥271MPa, and a room temperature impact strength AK. v2 ≥24J.

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