A continuous casting round billet for power station seamless steel pipe, a method for producing the same, and a power station seamless steel pipe and a method for producing the same

Abstract

This invention discloses a continuously cast round billet suitable for skew rolling of seamless steel pipes for thermal power plants and its continuous casting method, as well as a seamless steel pipe for thermal power plants and its production method. The continuously cast round billet contains C, Cr, Ni, W, and N, wherein A = Cr + W - 2 × Ni - 60 × (C + N), A ≥ 0.50; Y = Ni - 1.5 × C, Y ≥ 0.15; the central equiaxed crystal area ratio of the continuously cast round billet is ≤ 24%, the equiaxed crystal ratio is small, the billet segregation is small, and it is suitable for skew rolling process to manufacture seamless steel pipes. The seamless steel pipe for thermal power plants obtained by heat treatment after skew rolling has excellent high-temperature strength and a flaw detection pass rate ≥ 99.5%, meeting the needs of high-parameter thermal power plant construction.

Description

Technical Field

[0001] This invention belongs to the technical field of high alloy heat-resistant steel, specifically relating to a continuous casting round billet suitable for skew rolling of seamless steel pipes for thermal power plants and its continuous casting method, as well as a seamless steel pipe for thermal power plants and its production method. Background Technology

[0002] Thermal power, as my country's basic and guaranteed power source, has seen its installed capacity continuously increase in recent years. However, under pressure to conserve energy and reduce carbon emissions, thermal power is developing towards ultra-supercritical units with high temperature, high pressure, and high parameters. This change places higher demands on the high-grade boilers required for thermal power units.

[0003] On the one hand, the high-temperature strength requirements for seamless steel pipes used in boilers have increased, from the original 620℃ high-temperature strength to the test 650℃ high-temperature strength. On the other hand, the cost pressure of thermal power plant construction has increased sharply. Previously, steel ingots were used as raw materials to forge round steel to manufacture seamless steel pipes. Now, continuously cast round billets are used instead of steel ingots + forging as raw materials to manufacture seamless steel pipes.

[0004] When using continuous casting round billets to manufacture seamless steel pipes through skew rolling, the stress during skew rolling is spiral, which generates large radial tensile stress in the wall thickness direction of the steel pipe raw material. This makes the steel pipe prone to defects, resulting in unqualified flaw detection and failure to meet delivery requirements.

[0005] Chinese patent CN120079721A discloses a manufacturing method and product of ultra-large 9Cr series ferritic heat-resistant seamless steel pipe. This patent details the smelting process of the seamless steel pipe raw materials, but does not describe the continuous casting process that affects the equiaxed crystals at the center of the continuously cast billet. Furthermore, the patent's composition is based on standard requirements and has not been rationally adjusted; the high-temperature performance test temperature is 625℃, lacking a 650℃ high-temperature performance test.

[0006] Chinese patent CN114406003A discloses a method for preparing high-grade ultra-supercritical boiler tubes, but this patent mainly protects austenitic stainless steel for thermal power plants and does not involve martensitic heat-resistant steel for ultra-supercritical power plants.

[0007] Chinese patent CN118926493A discloses a casting method for ultra-large-sized ultra-supercritical P92 round steel. The patent focuses on controlling continuous casting speed, straightening coefficient, and electromagnetic stirring to keep the center crack of the continuously cast billet within level 2.5. However, it does not elaborate on the control of equiaxed crystals in the center of the continuously cast billet or the product's performance requirements for application.

[0008] Chinese patent CN116356200A discloses a heat-resistant steel for boiler tubes, its production method, and its application. This patent achieves high strength by adding rare elements, but the large number of alloying elements in this patent leads to increased costs, and it does not conduct relevant quality evaluation on the produced continuous casting billet products.

[0009] Therefore, in response to the above problems, it is urgent to solve the quality problems that occur when seamless steel pipes for thermal power plants are manufactured by skew rolling. This patent achieves a small proportion of equiaxed crystals in the center of the continuously cast billet, small segregation of the billet, and a high pass rate of the final product flaw detection through innovative component design, smelting and continuous casting control, thus meeting the needs of high-parameter thermal power plant construction. Summary of the Invention

[0010] To solve the above-mentioned technical problems, the present invention provides a continuously cast round billet suitable for skew rolling of seamless steel pipes for thermal power plants and a continuous casting method thereof. The central equiaxed crystal area ratio of the continuously cast round billet is ≤24%, the equiaxed crystal ratio is small, the billet segregation is small, and it is suitable for skew rolling process to manufacture seamless steel pipes.

[0011] The present invention also provides a seamless steel pipe for thermal power plants and its production method. The pipe is obtained by heat treatment after continuous casting of round billets as described in the present invention through skew rolling. The seamless steel pipe for thermal power plants has excellent high-temperature strength and a flaw detection pass rate of ≥99.5%, which meets the construction needs of high-parameter thermal power plants.

[0012] The technical solution adopted in this invention is as follows:

[0013] This invention provides a continuously cast round billet suitable for skew-rolled seamless steel pipes for thermal power plants. The continuously cast round billet contains, by weight percentage: C 0.07%–0.13%, Cr 8.50%–9.00%, Ni 0.20%–0.40%, W 1.60%–1.90%, and N 0.040%–0.070%, wherein the chemical composition ratio conforms to:

[0014] A=Cr+W-2×Ni-60× (C+N), A≥0.50;

[0015] Y = Ni - 1.5 × C, Y ≥ 0.15;

[0016] In the above formula, the value of each component is its content in steel × 100.

[0017] The area ratio of equiaxed crystals in the center of the continuously cast round billet is ≤24%, the segregation of columnar crystals and equiaxed crystals is ±0.025%~±0.040%, and the segregation range is 0.06%~0.09%.

[0018] This invention also provides a continuous casting method for the continuous casting of round billets suitable for skew rolling of seamless steel pipes for thermal power plants, wherein the billet diameter D, casting speed LS, cooling water volume WS, and superheat T satisfy the following conditions:

[0019] LS=40364 / ((D / 2) (D / 2))-T / 1000;

[0020] WS=0.15× (D / 2) × (D / 2) × LS+100×T;

[0021] Where D is in mm, LS is in m / min, WS is in L / mm, and T is in °C.

[0022] The present invention also provides a seamless steel pipe for thermal power plants, which is obtained by heat treatment after skew rolling of the continuously cast round billet as described in the present invention.

[0023] At half the wall thickness of the seamless steel pipe for thermal power plants, the yield strength at 650℃ is ≥248MPa, the KV2 at room temperature is ≥170J, and the flaw detection pass rate is ≥99.5%.

[0024] The microstructure of the seamless steel pipe for thermal power plants is martensite.

[0025] The present invention also provides a method for producing the aforementioned seamless steel pipe for thermal power plants, the method comprising the following steps: continuous casting billet blanking → continuous casting billet drilling → skew rolling tube → continuous rolling diameter reduction → air cooling → rough inspection of steel pipe → normalizing → tempering → mechanical inspection → finishing.

[0026] The normalizing process is as follows: normalizing temperature 1000-1050℃, holding time 1.5-2.5h, and spray cooling.

[0027] The tempering process adopts a stepped tempering method, which involves holding at 785~795℃ for 0.5~1.5h, then cooling with the furnace to 725~735℃, holding for 2.5~3.5h, and then air cooling after removal from the furnace.

[0028] The wall thickness of the seamless steel pipe for thermal power plants is ≥85mm.

[0029] The functions and controls of each component in the continuously cast round billet suitable for skew-rolled seamless steel pipes for thermal power plants provided by this invention are as follows:

[0030] C: C is the cheapest strengthening element in steel. Each 0.01% increase in dissolved C can increase strength by approximately 45 MPa. C forms precipitates with alloying elements in steel, resulting in precipitation strengthening. However, C tends to segregate and graphitize at high temperatures, thus reducing material strength. Therefore, the C content is controlled between 0.07% and 0.13%.

[0031] Cr: Cr is a major element in heat-resistant steel, improving its high-temperature oxidation resistance. Additionally, Cr belongs to the same group as Fe and can form substitution strengthening in steel. Cr can form compounds with C, providing strengthening at room temperature; however, during high-temperature service, carbides coarsen, and high Cr content can lead to the formation of the Rauss phase, which is detrimental to the high-temperature performance of the steel. The Cr content should be controlled between 8.50% and 9.00%.

[0032] Ni: Increasing the Ni equivalent in heat-resistant steel is beneficial for controlling high-temperature ferrite in the steel. However, at high temperatures, Ni can reduce lattice displacement resistance, causing deformation and thus reducing high-temperature strength. Ni significantly lowers the ductile-brittle transition temperature of steel and improves low-temperature toughness. Ni is a precious metal element, and excessive addition leads to excessively high costs. The Ni content should be controlled between 0.20% and 0.40%.

[0033] W: W is the most important element for enhancing high-temperature strength, and it can improve the red hardness and hot strength of steel. However, excessive W content will aggravate segregation and cause an increase in high-temperature ferrite in steel. Therefore, the W content is controlled between 1.60% and 1.90%.

[0034] Nitrogen (N): Nitrogen is the main compound-forming element in steel. This steel contains a large number of alloying elements, requiring sufficient nitrogen to form compounds. Therefore, the nitrogen content is controlled between 0.040% and 0.070%.

[0035] Seamless steel pipes for thermal power plants require high high-temperature strength. Since the deformation of continuously cast billets during seamless pipe manufacturing is relatively small, especially when using skew rolling, it is necessary to optimize the composition of the raw materials for skew rolling, focusing on improving the high-temperature strength and toughness of the steel. In the continuously cast round billets provided by this invention, Cr and W can improve the high-temperature strength of the steel, and these two elements are present in the highest concentrations, hence the high-temperature strength improvement coefficient is 1. Ni can reduce the high-temperature lattice shift resistance of the steel, thus negatively impacting high-temperature strength, with a strength influence coefficient of -2. C is the main element for graphitization, and N can promote graphitization in steel, which is detrimental to the strength of the steel at high temperatures, hence the influence coefficient is -60. Let the strengthening factor in the steel be represented by A, and control A ≥ 0.50.

[0036] A = Cr + W - 2 × Ni - 60 × (C + N).

[0037] Heat-resistant steel's toughness gradually decreases during service, therefore it requires a high toughness reserve. Ni (Ni) at room temperature reduces the activation energy of stacking fault displacement in steel, making deformation more coordinated and thus improving toughness; therefore, its toughness contribution coefficient is 1. Carbon (C) is the main element affecting steel toughness. Because C significantly increases the room temperature strength of steel, it is detrimental to toughness; therefore, its influence coefficient is -1.5. Let the toughness factor in steel be represented by Y, then Y ≥ 0.15, Y = Ni - 1.5 × C.

[0038] The production process of continuously cast round billets suitable for skew rolling of seamless steel pipes for thermal power plants provided by the present invention is as follows: smelting in an electric arc furnace or converter → refining in an LF furnace → RH or VD vacuum degassing → continuous casting of round billets ≥φ380mm → slow cooling of round billets → annealing of round billets.

[0039] The key factors for controlling equiaxed crystals and segregation in the center of the continuously cast billet are casting speed (LS), cooling water volume (WS), and superheat (T). For continuously cast billets of different diameters (D), these key factors need to be controlled. This invention controls LS = 40364 / ((D / 2) - T / 1000) to ensure a low proportion of equiaxed crystals and minimal segregation in the center of the continuously cast billet.

[0040] During continuous casting, the amount of cooling water affects the central equiaxed grains and surface quality of the billet. Because heat-resistant steel contains high levels of Nb and V, excessive cooling water can cause surface cracks in the billet, leading to crack propagation during subsequent straightening and ultimately resulting in cracks on the outer wall of the skew-rolled tube, causing defects in flaw detection. Insufficient cooling water not only causes steel leakage during solidification but also results in excessively large central equiaxed grains, increasing tensile stress during skew-rolled tube production and causing defects such as delamination in the steel tube. This invention controls the amount of cooling water during continuous casting by controlling WS = 0.15 × (D / 2) × (D / 2) × LS + 100 × T, thereby controlling the proportion of central equiaxed grains and the surface quality of the continuously cast billet.

[0041] To improve the high-temperature strength of seamless steel pipes for thermal power plants, this invention also controls the tempering process of the steel pipe, employing a stepped tempering method. This allows for control over the type and size of carbide precipitation in the steel. By holding the steel at different temperature stages, the desired carbides can be precipitated. However, excessively long holding times at high temperatures can lead to increased carbide size, while holding at low temperatures can prevent excessive size. Therefore, this invention uses a high-temperature precipitation and low-temperature growth method to refine the precipitated phases in the steel.

[0042] The annealing process for round billets is as follows: first, the temperature is raised to 450-550℃ and held for 4-6 hours; then, the temperature is raised to 750-800℃ and held for 36-48 hours; finally, the billets are cooled in the furnace. Compared with the prior art, this invention has the following beneficial effects:

[0043] This invention optimizes the proportions of C, Cr, Ni, W, and N elements in continuously cast round billets, and comprehensively controls C, Cr, Ni, W, and N in formula A, and controls Ni and C in formula Y, thereby ensuring the quality of continuously cast round billets and the high-temperature strength and toughness of the seamless steel pipes produced.

[0044] In the continuous casting process of continuously cast round billets, this invention determines the continuous casting speed LS=40364 / ((D / 2)(D / 2))-T / 1000 based on the billet diameter D and the superheat of the molten steel T, and determines the cooling water volume WS=0.15×(D / 2)×(D / 2)×LS+100×T based on the billet diameter D, the molten steel superheat T, and the continuous casting speed LS. Under appropriate casting speed and cooling water volume, a continuously cast billet with a small proportion of central equiaxed crystals, less segregation, and good surface quality is obtained, which provides a strong guarantee for the subsequent skew rolling preparation of seamless steel pipes for thermal power plants.

[0045] This invention improves the high-temperature strength of seamless steel pipes by employing a stepped tempering process.

[0046] The seamless steel pipe for thermal power plants provided by this invention has a yield strength of ≥248MPa at 650℃ and KV2 ≥170J at room temperature at 1 / 2 wall thickness, and a flaw detection pass rate of ≥99.5%. Attached Figure Description

[0047] Figure 1 The low-magnification microstructure of the continuously cast round billet in Example 1;

[0048] Figure 2 The low-magnification microstructure of the continuously cast round billet in Example 2;

[0049] Figure 3 The low-magnification microstructure of the continuously cast round billet in Example 3;

[0050] Figure 4 The microstructure of the continuously cast round billet in Comparative Example 1 is shown in low magnification.

[0051] Figure 5 The microstructure of the continuously cast round billet in Comparative Example 2 is shown in low magnification.

[0052] Figure 6 The microstructure of the continuously cast round billet in Comparative Example 3 is shown in low magnification.

[0053] Figure 7 The microstructure of the continuously cast round billet in Comparative Example 4 is shown in low magnification.

[0054] Figure 8 The microstructure of the continuously cast round billet in Comparative Example 5 is shown in low magnification.

[0055] Figure 9 The image shows the metallographic structure of the seamless steel pipe for thermal power plants in Example 2.

[0056] Figure 10 The image shows the metallographic structure of the seamless steel pipe for thermal power plants in Comparative Example 5. Detailed Implementation

[0057] This invention provides a continuously cast round billet suitable for skew-rolled seamless steel pipes for thermal power plants, containing, by weight percentage: C 0.07%–0.13%, Cr 8.50%–9.00%, Ni 0.20%–0.40%, W 1.60%–1.90%, and N 0.040%–0.070%, wherein the chemical composition ratio conforms to:

[0058] A=Cr+W-2×Ni-60× (C+N), A≥0.50;

[0059] Y = Ni - 1.5 × C, Y ≥ 0.15;

[0060] In the above formula, each component is represented by its content in the steel multiplied by 100.

[0061] The production process of the continuously cast round billet is as follows: smelting in an electric arc furnace or converter → refining in an LF furnace → vacuum degassing in an RH or VD furnace → continuous casting of round billets ≥ φ380mm → slow cooling of round billets → annealing of round billets; in the continuous casting step, the billet diameter D, casting speed LS, cooling water volume WS, and superheat T satisfy the following conditions:

[0062] LS=40364 / ((D / 2) (D / 2))-T / 1000;

[0063] WS=0.15× (D / 2) × (D / 2) × LS+100×T;

[0064] Where D is in mm, LS is in m / min, WS is in L / mm, and T is in °C.

[0065] The round billet annealing process is as follows: first, heat to 450-550℃ and hold for 4-6 hours, then heat to 750-800℃ and hold for 36-48 hours, and then cool with the furnace.

[0066] The continuous casting round billet is heat-treated after oblique rolling to obtain a seamless steel pipe for thermal power generation. The production process is as follows: continuous casting billet blanking → continuous casting billet drilling → oblique rolling → continuous rolling diameter reduction → air cooling → rough inspection of steel pipe → normalizing → tempering → mechanical inspection → finishing. Among them, the normalizing process is: normalizing temperature 1000-1050℃, holding time 1.5-2.5h, spray cooling; the tempering adopts stepped tempering, the process is: holding at 785~795℃ for 0.5~1.5h, then cooling in the furnace to 725~735℃, holding for 2.5~3.5h, and then air cooling after exiting the furnace; the wall thickness of the produced seamless steel pipe for thermal power generation is ≥85mm.

[0067] The present invention will now be described in detail with reference to the embodiments.

[0068] The chemical composition and weight percentage of the continuously cast round billets in each embodiment and comparative example are shown in Table 1.

[0069] Table 1

[0070]

[0071] The continuously cast round billets in each embodiment and comparative example are produced using the following process:

[0072] Electric furnace / converter smelting: oxygen is determined before tapping, and steel is left in place during tapping to avoid slag discharge;

[0073] LF furnace: C, Si, Mn, Cr, Ni, Mo, V, Nb, W, B, N and other elements are adjusted to the target values;

[0074] Vacuum degassing: Pure degassing time ≥ 20 minutes, ensuring that the [H] content after vacuum treatment is ≤ 1.0 ppm, and avoiding white spots in the steel;

[0075] Continuous casting: The target temperature of molten steel in the ladle is controlled at 10~40℃ above the liquidus temperature. Taking a φ700mm continuous casting round billet as an example, the key processes of continuous casting are shown in Table 2.

[0076] Table 2

[0077]

[0078] After continuous casting, the billet is annealed using the following process: first, the temperature is raised to 500℃ and held for 5 hours, then the temperature is raised to 780℃ and held for 42 hours, and then cooled with the furnace.

[0079] Table 3 shows the proportion of central equiaxed crystals, segregation of columnar crystals and equiaxed crystals, and segregation range of continuous casting round billets in each embodiment and comparative example. In the table, the segregation of columnar crystals and equiaxed crystals refers to the difference in carbon element mass fraction segregation between the columnar crystal region and the central equiaxed crystal region.

[0080] Table 3

[0081]

[0082] Seamless steel pipes were manufactured from the continuously cast round billets in the various embodiments and comparative examples according to the following process: continuous casting round billet blanking → continuous casting round billet drilling → skew rolling tube → continuous rolling diameter reduction → air cooling → rough inspection of steel pipe → normalizing → tempering → mechanical inspection → finishing. The process parameters for normalizing and tempering are shown in Table 4.

[0083] Table 4

[0084]

[0085] Performance tests were conducted on the seamless steel pipes produced in each embodiment and comparative example. Tensile and impact specimens were taken from half the thickness of the pipes and tested according to GB / T 228.2-2015 "Metallic materials – Tensile testing – Part 2: High temperature test method", GB / T 229-2020 "Metallic materials – Charpy impact test method", and GB / T 5777-2019 "Automatic full-circumferential ultrasonic testing of longitudinal and / or transverse defects in seamless and welded (excluding submerged arc welded) steel pipes". The test results are shown in Table 5.

[0086] Table 5

[0087]

[0088] As can be seen from the above, when continuously cast round billets are produced according to the chemical composition and continuous casting process required by this application, the proportion of equiaxed crystals in the center of the continuously cast round billet is ≤24%, the segregation of columnar crystals and equiaxed crystals is ±0.025%~±0.040%, the segregation range is 0.06%~0.09%, and the seamless steel pipe produced therefrom is tempered according to the tempering process required by this invention. The yield strength at 650℃ at 1 / 2 thickness of the seamless steel pipe is ≥248MPa, the room temperature KV2 is ≥170J, and the flaw detection pass rate is ≥99.5%.

[0089] In Comparative Example 1, during the continuous casting process, the casting speed and cooling water volume were not controlled according to the requirements of this invention: LS=40364 / ((D / 2) (D / 2))-T / 1000 and WS=0.15× (D / 2) × (D / 2) LS+100×T, resulting in a slightly lower flaw detection pass rate for the final seamless steel pipe.

[0090] In Comparative Examples 2 and 3, although the C, Cr, Ni, W, and N contents of the continuously cast round billets were controlled according to the requirements of this invention, Ni and C were not controlled according to Y=Ni-1.5×C, Y≥0.15. Furthermore, the tempering of the seamless steel pipe in Comparative Example 3 was carried out according to the tempering process required by this invention. This resulted in a high proportion of equiaxed crystals in the center of the continuously cast round billets, large segregation of columnar and equiaxed crystals, and a large segregation range. Consequently, the high-temperature strength, toughness, and flaw detection pass rate of the seamless steel pipes produced were all poor.

[0091] In Comparative Examples 4 and 5, although the C, Cr, Ni, W, and N contents of the continuously cast round billets were controlled according to the requirements of this invention, the C, Cr, Ni, W, and N contents were not controlled according to A=Cr+W-2×Ni-60×(C+N), where A≥0.50. Furthermore, the tempering of the seamless steel pipe in Comparative Example 4 was carried out according to the tempering process required by this invention. This resulted in a high proportion of equiaxed crystals in the center of the continuously cast round billets, large segregation of columnar and equiaxed crystals, and a large segregation range. Consequently, the high-temperature strength, toughness, and flaw detection pass rate of the final seamless steel pipe were all poor.

[0092] The low-magnification microstructure of the continuously cast round billets in Examples 1-3 is as follows: Figure 1-3 As shown in the figure, the various structures in the low-magnification pickled structure are evenly distributed along the geometric center. The proportion of equiaxed crystals in the center is small, the columnar crystal structure is fine, and the columnar crystals as a whole show growth towards the center with a small angle to the diameter.

[0093] The low-magnification microstructure of the continuously cast round billets in Comparative Examples 1-5 is as follows: Figure 4-8 As shown in the figure, the proportion of central equiaxed crystals in the low-magnification acid-washed microstructure is relatively large, and the microstructure shows deviations from the geometric center, with well-developed columnar crystals on one side. Furthermore, the columnar crystals form a large angle with the diameter direction and are distributed in a spiral pattern.

[0094] Figure 9 The image shows the metallographic structure of the seamless steel pipe for thermal power plants in Example 2. As can be seen from the image, the finished steel pipe has a fine microstructure, uniform martensite morphology, and uniformly dispersed precipitates.

[0095] Figure 10 The image shows the metallographic structure of the seamless steel pipe for thermal power plants in Comparative Example 5. As can be seen from the image, in comparison with... Figure 9 At the same multiple, its microstructure is relatively coarse, with large grain boundaries and insufficiently fine precipitates.

[0096] The above-described detailed description of a continuously cast round billet suitable for skew-rolled seamless steel pipes for thermal power plants and its continuous casting method, as well as a seamless steel pipe for thermal power plants and its production method, is illustrative rather than limiting. Several embodiments can be listed according to the defined scope. Therefore, changes and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A continuously cast round billet suitable for use in the production of a power plant seamless steel pipe by skew rolling, characterized in that, The continuous casting round billet contains, by weight percentage, C 0.07%-0.13%, Cr 8.50%-9.00%, Ni 0.20%-0.40%, W 1.60%-1.90%, N 0.040%-0.070%, wherein the chemical component ratio meets: A=Cr+W-2xNi-60x(C+N), A≥0.50; Y=Ni-1.5xC, Y≥0.15; In the above formula, the value of each component is the content of it in the steel x 100.

2. The continuously cast round billet suitable for use in cross rolling for the production of a power plant seamless steel pipe according to claim 1, characterized in that, The center equiaxed crystal area ratio of the continuous casting round billet is ≤24%, the columnar crystal and equiaxed crystal segregation is ±0.025%-±0.040%, and the segregation range is 0.06%-0.09%.

3. The continuous casting method of a continuous casting round billet suitable for cross rolling for the production of a power plant seamless steel pipe according to claim 1 or 2, characterized in that, The billet diameter D, the drawing speed LS, the cooling water amount WS, and the superheat T meet: LS=40364 / ((D / 2) (D / 2))-T / 1000; WS=0.15x (D / 2) x (D / 2) x LS+100x T; wherein the unit of D is mm, the unit of LS is m / min, the unit of WS is L / mm, and the unit of T is ℃.

4. A seamless steel tube for a thermal power plant, characterized by, The thermal power seamless steel pipe is obtained by adopting the continuous casting round billet of claim 1 or 2 after pipe rolling and heat treatment.

5. The seamless steel pipe for a thermal power plant according to claim 4, characterized by The yield strength at 650 ℃ of the thermal power seamless steel pipe at 1 / 2 wall thickness is ≥248 MPa, the room temperature KV2 is ≥170 J, and the flaw detection qualified rate is ≥99.5%.

6. The seamless steel pipe for a thermal power plant according to claim 4, wherein The metallographic structure of the thermal power seamless steel pipe is martensite.

7. The method of producing a power plant seamless steel pipe according to claim 4, characterized by, The production method comprises the following steps: continuous casting billet blanking, continuous casting billet punching, pipe rolling, continuous rolling and reducing, air cooling, steel pipe rough flaw detection, normalizing, tempering, mechanical inspection, and finishing.

8. The production method according to claim 7, characterized by, The normalizing process is: normalizing temperature 1000-1050 ℃, holding time 1.5-2.5 h, and spray cooling.

9. The production method according to claim 7, characterized by, The tempering adopts step tempering, and the process is: 785-795 ℃ holding for 0.5-1.5 h, then furnace cooling to 725-735 ℃, holding for 2.5-3.5 h, and then air cooling after furnace discharge.

10. The production method according to claim 7, characterized by, The wall thickness of the thermal power seamless steel pipe is ≥85 mm.

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