CN114182083B - Method for improving impact toughness of 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel tube - Google Patents
Method for improving impact toughness of 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel tube Download PDFInfo
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Abstract
The application provides a method for improving impact toughness of a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel tube, which sequentially comprises the following steps: alloy smelting, tube blank preparation, tube making, normalizing, tempering pretreatment and tempering heat treatment; wherein, in the tempering pretreatment procedure, the heat preservation temperature of the tempering pretreatment is 400-600 ℃, and the tempering pretreatment is carried out in air after heat preservation; the method can avoid the concentrated precipitation of the multi-element trace alloy elements in the areas where elements are easy to gather, such as grain boundaries and the like, by the heat treatment of the prior standard requirements (normalizing and tempering), thereby improving the metallographic structure and the precipitate form after the heat treatment, and improving the toughness of the steel pipe and the homogeneity of the thick-wall steel pipe.
Description
Technical Field
The application belongs to the field of heat-resistant steel manufacturing, and particularly relates to a method for improving impact toughness of a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel tube.
Background
ASME SA 213T 23/SA 335P 23 (2.25 Cr-1.6W-V-Nb) is prepared by improving components of Japanese Sumitomo company on the basis of heat-resistant steel grade steel G102 of China power station to form W-Mo-V composite solid solution strengthening mainly containing W, adding trace Nb and N elements to form carbonitride (mainly VC, VN, M) 23 C 6 And M 7 C 3 ) And the novel low-alloy bainite heat-resistant steel with low cost and high strength is prepared through dispersion precipitation strengthening. The steel is mainly used for manufacturing pipes for parts such as heating surfaces, pressure pipelines, headers and the like of large-scale power station boilers.
In the early-stage application in China, a T23 (lower caliber) steel pipe is mainly adopted as a water cooling wall for a power station boiler. In application, it is found that in the manufacturing process and in operation, welding cracks and reheating cracks are easily generated at the position of a welded junction heat affected zone to cause frequent occurrence of quality accidents, so that the power station industry is generally not full, users start to reject the T23 steel pipe as a water-cooled wall pipe in succession, the T23 steel pipe is gradually abandoned by the boiler and the power industry, and the application of the P23 (large-caliber thick-wall) steel pipe is also stagnated.
Cracks occurring in the weld heat affected zone and reheat cracks occurring during operation, although in the welding crack field both cracks are of the cold type, and the reheat cracks are of the hot type. However, the cracking mechanism is not released or inhibited in the restraint stress, the shaping reserve of the base metal and the surrounding area of the heat affected zone is insufficient, and delayed cracks are generated under the adverse condition that local stress concentration is caused by trace element segregation or local precipitation of precipitates; in the subsequent thermal operation state, trace elements are precipitated at weak positions such as grain boundaries to reduce the high-temperature strength of the region, and reheat cracks are formed under the influence of external factors such as structural stress. Cr, mo, V, nb, ti, B and the like in the T23 steel pipe are strong carbide forming elements, and have a great influence on reheat crack formation. If the content of harmful low melting points such as sulfur, phosphorus and the like is not strictly controlled in smelting, reheat cracks are more likely to occur, and the tendency of cracking is greater for P23 large-caliber thick-wall pipes due to the existence of size effects.
At present, T23/P23 steel pipes obtained by the manufacturing method according to the prior standard requirements (GB/T5310-2017) have the finished product impact value lower or slightly higher than the normal user requirements A KV And the impact absorption power test value is equal to or more than 27J. Such low impact values can create a very large uncertainty for both product manufacture and later safe operation, not to mention safety assurance. Therefore, in the hot working procedure in the steel pipe manufacture, the control of the embrittlement behavior possibly generated by the T23/P23 is very beneficial to ensuring the toughness and good welding manufacturability of the T23/P23 material, and meanwhile, the method has very important significance in the reapplication of the T23 steel pipe on parts such as a water cooling wall of a thermal power generating unit and the popularization of the P23 steel pipe on parts such as a pressure pipeline and a header after overcoming the embrittlement behavior of the original material of the T23/P23 steel pipe.
Disclosure of Invention
Aiming at the defects of the prior art, the application aims to provide a method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe, which is characterized in that the normalized seamless steel pipe is subjected to tempering pretreatment and then tempering heat treatment so as to obtain the 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe; according to the application, tempering pretreatment is carried out firstly, so that multielement trace alloy elements are uniformly and diffusely separated out in a plurality of areas in a martensite/bainite matrix at a lower temperature, and then the size and the number of the precipitates are further increased through tempering heat treatment at a higher temperature, so that the dislocation density in the martensite/bainite matrix is reduced; the method can avoid the concentrated precipitation of the multi-element trace alloy elements in the areas where elements are easy to gather, such as grain boundaries and the like, by the heat treatment of the prior standard requirements (normalizing and tempering), thereby improving the metallographic structure and the precipitate form after the heat treatment, and improving the toughness of the steel pipe and the homogeneity of the thick-wall steel pipe.
In order to achieve the above purpose, the present application adopts the following technical scheme:
a method for improving impact toughness of a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel tube sequentially comprises the following steps: alloy smelting, tube blank preparation, tube making, normalizing, tempering pretreatment and tempering heat treatment;
wherein, in the tempering pretreatment process, the temperature of the tempering pretreatment is 400 ℃ -600 ℃ (such as 450 ℃, 480 ℃, 500 ℃, 550 ℃, 580 ℃), and the tempering pretreatment is carried out in air after the heat preservation.
In the above method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe, as a preferred embodiment, in the tempering pretreatment step, the number of times of tempering pretreatment is 3 or less; preferably, the tempering pretreatment is performed twice.
In the present application, by performing tempering pretreatment after the normalizing process and before the tempering heat treatment process, the purpose is to continue transformation of a small amount of residual austenite, which has not yet been transformed, into martensite or bainite in the 2.25Cr-1.6W-V-Nb seamless steel pipe; in addition, the tempering pretreatment is carried out at 400-600 ℃, so that the precipitates of carbon and nitride such as V, nb, ti and the like can be precipitated in situ, and further grow up (nano distance) in a small area range, the dispersion distribution of the precipitates and the good matching of the toughness of nano-sized fine precipitates (V, nb, ti and C, N) are realized, the toughness of the steel pipe is further enhanced, and meanwhile, the rapid growth of the precipitates and the large-scale migration to grain boundaries can be prevented, so that the embrittlement of the material is caused; through tempering pretreatment for more than two times (not more than three times), the dispersion degree of the precipitate is more uniform, the number of particles is more, and the effective control of material homogenization is more facilitated; the manufacturing method can avoid direct tempering heat treatment in the existing standard cone manufacturing process, and the multi-element trace alloy elements are rapidly concentrated and separated out in the areas where elements are easy to gather, such as grain boundaries, so that the metallurgical structure and the form of the separated out matters after normalizing can be improved, and the toughness of the steel pipe and the homogeneity of the thick-wall steel pipe are improved. In the application, the tempering pretreatment temperature is higher than 600 ℃ or lower than 400 ℃ and the improvement range of the impact toughness of the 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe is small or not obviously improved.
In the above method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat resistant alloy seamless steel pipe, as a preferred embodiment, in the tempering pretreatment step, the soaking time is 3min/mm (minutes/wall thickness).
Specifically, the manufacturing method of the application comprises the following steps:
alloy smelting process: smelting alloy molten steel by adopting an electric furnace smelting, external refining and vacuum degassing smelting process;
a tube blank preparation process: making the alloy molten steel into a tube blank through casting, forging or continuous casting processes;
tubulation process: heating the tube blank in a heating furnace, and obtaining a steel tube through hot rolling;
normalizing process: fully heating and preserving the heat of the steel pipe in a heating furnace to ensure that the steel pipe is completely austenitized, and then carrying out rapid cooling treatment;
tempering pretreatment: placing the steel pipe obtained through the rapid cooling treatment into a heat treatment furnace for tempering pretreatment, controlling the heat preservation temperature of the tempering pretreatment to be 400-600 ℃, and cooling in air after heat preservation;
tempering heat treatment: and placing the steel pipe obtained by tempering pretreatment into a heat treatment furnace for tempering heat treatment.
In the above method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat resistant alloy seamless steel pipe, as a preferred embodiment, in the normalizing step, the normalizing holding temperature is 1040 to 1180 ℃ (e.g., 1060 ℃, 1080 ℃, 1100 ℃, 1120 ℃, 1140 ℃, 1160 ℃), and the soaking time is 1.5min/mm (min/wall thickness).
In the above method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe, as a preferred embodiment, in the normalizing step, a rapid cooling treatment is performed to 400 ℃ or lower, more preferably to room temperature; preferably, the cooling rate is greater than or equal to 50 ℃/min, more preferably greater than or equal to 300 ℃/min; preferably, the rapid cooling treatment is water-cooled or water mist cooled.
In the application, rapid cooling treatment is carried out in the normalizing process, so that the precipitation and diffusion of multi-element trace alloy elements and small-size atoms such as carbon, boron, nitrogen and the like along grain boundaries can be inhibited; in the application, the rapid cooling treatment and tempering pretreatment in the normalizing process are key processes for improving the toughness level of the material. If the rapid cooling treatment is not performed in the normalizing process, precipitates are precipitated along grain boundaries, so that the impact toughness of the manufactured 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe is greatly reduced, and the precipitates are prevented from being precipitated along the grain boundaries by performing the rapid cooling treatment in the normalizing process, so that a foundation is laid for subsequently improving the impact toughness of the seamless steel pipe.
In the above method for improving the impact toughness of a seamless steel pipe of a 2.25Cr-1.6W-V-Nb heat-resistant alloy, as a preferred embodiment, in the tempering heat treatment step, the tempering heat preservation temperature is 730 ℃ -800 ℃ (such as 740 ℃, 750 ℃, 760 ℃, 770 ℃, 780 ℃) and the soaking time is 2.5min/mm (minutes/wall thickness).
In the above method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe, as a preferred embodiment, in the tempering heat treatment step, a rapid cooling treatment is performed; preferably, the cooling rate is more than or equal to 50 ℃/min; preferably, the rapid cooling treatment is water-cooled, water mist-cooled or air-cooled.
In the application, if slow cooling is adopted in the tempering heat treatment process, the strength requirement of the 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe is not guaranteed, and the higher impact toughness is maintained.
In the method for improving the impact toughness of the 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe, as a preferred embodiment, the seamless steel pipe comprises the following elements in percentage by mass: 0.04 to 0.10 percent of C, less than or equal to 0.50 percent of Si, 0.10 to 0.60 percent of Mn, less than or equal to 0.030 percent of P, less than or equal to 0.010 percent of S, 1.90 to 2.60 percent of Cr, 0.050 to 0.30 percent of Mo, 0.20 to 0.30 percent of V, 0.02 to 0.08 percent of Nb, less than or equal to 0.010 percent of N, less than or equal to 0.030 percent of Al, 1.45 to 1.75 percent of W, 0.002 to 0.006 percent of B, 0.010 to 0.060 percent of Ti, less than or equal to 0.40 percent of Ni, and the balance of Fe and unavoidable impurities.
In the method for improving the impact toughness of the 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel tube, as a preferable embodiment, the outer diameter of the seamless steel tube is 51 mm-800 mm (such as 80mm, 150mm, 300mm, 500mm and 700 mm), and the wall thickness is 4.5 mm-150 mm (such as 10mm, 20mm, 30mm, 35mm, 45mm, 50mm, 70mm, 90mm, 110mm and 130 mm).
The second object of the application is to provide a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel tube which is prepared by adopting the method.
A2.25 Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe has yield strength of more than or equal to 400MPa, tensile strength of more than or equal to 510MPa, elongation after break of more than or equal to 20 percent and impact absorption power of more than or equal to 40J.
The application further aims to provide an application of the 2.25Cr-1.6W-V-Nb heat-resistant alloy steel pipe in an ultra-supercritical generator set, and the heat-resistant alloy steel pipe is used as an alloy pipe for a steam pipeline, a header component and a water-cooled wall.
Compared with the prior art, the application has the following positive effects:
(1) The application adopts the procedures of electric furnace/converter smelting, external refining, vacuum degassing, forging pipe blank, hot rolling pipe making, normalizing, tempering pretreatment and tempering heat treatment, thereby manufacturing the 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe; by carrying out tempering pretreatment after the normalizing process and before the tempering heat treatment process, precipitates of carbon, nb, ti and the like can be precipitated in situ, so that the precipitates grow in a small area range (nano-scale distance), the dispersion distribution of the precipitates and the toughness of nano-scale fine precipitates (V, nb, ti and C, N) are well matched, and the toughness of the steel pipe is further enhanced;
(2) The 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe obtained by the method has the yield strength of more than or equal to 400MPa, the tensile strength of more than or equal to 510MPa, the elongation after fracture of more than or equal to 20 percent and the impact absorption power of more than or equal to 40J.
(3) The 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel tube obtained by the method is applied to an ultra-supercritical generator set and is used as an alloy tube for a steam pipeline, a header component and a water-cooled wall.
Drawings
FIG. 1 is a metallographic structure diagram of a seamless steel pipe obtained in example 1 of the present application, which is 200 times larger;
FIG. 2 is a metallographic structure diagram of a seamless steel pipe according to example 1 of the present application, which is 500 times larger than that of the seamless steel pipe;
FIG. 3 is a metallographic structure diagram of a seamless steel pipe according to example 2 of the present application, which is a 200-fold magnification;
FIG. 4 is a metallographic structure diagram of a seamless steel pipe according to example 2 of the present application, which is 500 times larger than that of the seamless steel pipe;
FIG. 5 is a metallographic structure diagram of a seamless steel pipe according to comparative example 1 of the present application, which is a 200-fold magnification;
FIG. 6 is a metallographic structure diagram of a seamless steel pipe according to comparative example 1 of the present application, which is 500 times larger than that of the seamless steel pipe;
Detailed Description
Technical solutions in the embodiments of the present application will be clearly and completely described below to enable one skilled in the art to practice and reproduce the present application. All other embodiments, which are derived by a person skilled in the art based on the embodiments of the application, fall within the scope of protection of the application.
The alloy steel obtained by the alloy smelting process in the following examples has the brand of T23/P23 (chemical composition of 2.25 Cr-1.6W-V-Nb), and the mass percentages of the respective element compositions are shown in Table 1;
TABLE 1 mass percent of each element component (balance Fe and unavoidable impurities) in 2.25Cr-1.6W-V-Nb alloy steel
| C | Si | Mn | P | S | Cr | Mo | W | V | Nb | N | Al | B | Ni | Ti |
| 0.062 | 0.22 | 0.35 | 0.009 | 0.003 | 2.22 | 0.22 | 1.50 | 0.207 | 0.038 | 0.0065 | 0.001 | 0.0042 | 0.09 | 0.0314 |
Example 1
Alloy smelting process: smelting alloy molten steel by adopting an electric furnace smelting, external refining and vacuum degassing smelting process;
a tube blank preparation process: casting the molten alloy steel to obtain cast ingot, and forging the cast ingot into a cast ingotA tube blank;
tubulation process: heating the tube blank in an annular heating furnace, wherein the temperature of a soaking section is 1240 ℃, the temperature equalizing time is 3min/mm, and then adopting a 460 Azier hot rolling tube unit to prepare a pierced billet 389mm multiplied by 41.5mm (diameter multiplied by wall thickness);
normalizing process: heating the pierced billet in a step heating furnace to 1050 ℃ for uniform temperature, wherein the uniform temperature time is 1.5min/mm, and then cooling the pierced billet to room temperature by water mist, wherein the cooling rate is more than 50 ℃/min;
tempering pretreatment: placing the steel pipe obtained through the water mist cooling treatment in a step heating furnace for tempering pretreatment, wherein the heat preservation temperature of the tempering pretreatment is 560 ℃, the temperature equalization time is 3min/mm, and cooling to room temperature in air after heat preservation (the number of times of tempering pretreatment is one time);
tempering heat treatment: placing the steel pipe obtained by tempering pretreatment in a step heating furnace for tempering heat treatment, wherein the heat preservation temperature of the tempering heat treatment is 760 ℃, the temperature equalization time is 2.5min/mm, and then rapidly cooling to room temperature by adopting water cooling, and the cooling rate is more than 50 ℃/min;
obtaining a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel tube with the specification of 335.6mm (+ -5 mm) x 40mm (+ -3 mm) x 6.8m through an internal and external mechanical grinding process; fig. 1 and 2 show the metallographic structure of example 1, and it can be seen that the 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe obtained by the primary tempering pretreatment has fine and uniform carbide precipitation.
Example 2
In example 2, the number of tempering pretreatment in example 2 was two, which was the same as in example 1 except that the tempering pretreatment process was slightly different from that in example 1; fig. 3 and 4 show metallographic structures of example 2, and it can be seen from the diagrams that the 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel tube obtained after two tempering pretreatment has more dispersed, finer and more uniform carbide precipitated in the metallographic structures, which is very beneficial to improving comprehensive properties of the material and improving embrittlement tendency of the material.
Comparative example 1
Alloy smelting process: smelting alloy molten steel by adopting an electric furnace smelting, external refining and vacuum degassing smelting process;
a tube blank preparation process: casting the alloy molten steel to obtain an ingot, and forging the ingot into a tube blank with the diameter of 390 mm;
tubulation process: heating the tube blank in an annular heating furnace, wherein the temperature of a soaking section is 1240 ℃, the temperature equalizing time is 3min/mm, and then adopting a 460 Azier hot rolling tube unit to prepare a pierced billet 389mm multiplied by 41.5mm (diameter multiplied by wall thickness);
normalizing process: heating the pierced billet in a step heating furnace to 1050 ℃ for uniform temperature, wherein the uniform temperature time is 1.5min/mm, and then cooling to room temperature in air after heat preservation;
tempering heat treatment: and (3) placing the steel pipe obtained through the normalizing treatment in a step heating furnace for tempering heat treatment, wherein the heat preservation temperature of the tempering heat treatment is 760 ℃, the temperature equalization time is 2.5min/mm, and then cooling to room temperature in air after heat preservation.
A2.25 Cr-1.6W-V-Nb heat resistant alloy seamless steel pipe (whose metallographic structure is shown in FIG. 5 and FIG. 6) with a specification of 335.6mm (+ -5 mm). Times.40 mm (+ -3 mm). Times.6.8 m was obtained by an internal and external mechanical grinding process, and carbides precipitated in the metallographic structure were precipitated along grain boundaries and coarser than carbides precipitated in example 1.
Comparative example 2
Comparative example 2 was the same as example 1 except that the tempering pretreatment process was slightly different from example 1, and the tempering pretreatment temperature in comparative example 2 was 350 ℃. The comparative example adopts tempering pretreatment heat preservation temperature lower than 400 ℃, belongs to low-temperature tempering, basically has no precipitation of particles, does not control the size and precipitation position of the precipitate, and does not play a role in improving impact energy.
Comparative example 3
Comparative example 3 was the same as example 1 except that the tempering pretreatment process was slightly different from example 1, and the tempering pretreatment temperature in comparative example 3 was 650 ℃. In the comparative example, because the tempering pretreatment has higher heat preservation temperature, the concentrated precipitation of the multi-element trace alloy elements in the areas where elements are easy to gather, such as grain boundaries, cannot be avoided, the room temperature impact energy of the pipe cannot be improved, and the obtained pipe has low room temperature impact energy.
Performance testing
The seamless steel pipes of the heat-resistant alloy of 2.25Cr-1.6W-V-Nb obtained in examples 1 to 2 and comparative examples 1 to 3 were subjected to tensile test (center position of wall thickness was taken) (according to GB/T228.1-2010 "section 1 of tensile test for metallic materials: room temperature test method"), room temperature impact test (position of wall thickness was taken) (according to GB/T229-2020 "Charpy pendulum impact test method for metallic materials"), ultrasonic flaw detection test (automatic ultrasonic test of full circumference of longitudinal and/or transverse flaws of seamless and welded (excluding submerged arc welding) steel pipes according to GB/T5777-2019), eddy current flaw detection (automatic eddy current test of flaws of seamless and welded (excluding submerged arc welding) steel pipes according to GB/T7735-2018), respectively, and the test results are shown in Table 2.
TABLE 2 Performance data for seamless steel pipes of 2.25Cr-1.6W-V-Nb heat resistant alloy obtained in examples 1-2 and comparative examples 1-3 of the present application
The foregoing description of the preferred embodiments of the application is not intended to limit the application to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the application as defined by the appended claims.
Claims (11)
1. A method for improving impact toughness of a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel tube is characterized by comprising the following steps in sequence: alloy smelting, tube blank preparation, tube making, normalizing, tempering pretreatment and tempering heat treatment; wherein, in the tempering pretreatment procedure, the heat preservation temperature of the tempering pretreatment is 400-600 ℃, and the tempering pretreatment is carried out in air after heat preservation; the tempering pretreatment times are two times;
in the normalizing process, the cooling rate is more than or equal to 50 ℃/min;
the seamless steel pipe comprises the following elements in percentage by mass: 0.04% -0.10% of C, less than or equal to 0.50% of Si, 0.10% -0.60% of Mn, less than or equal to 0.030% of P, less than or equal to 0.010% of S, 1.90% -2.60% of Cr, 0.050% -0.30% of Mo, 0.20% -0.30% of V, 0.02% -0.08% of Nb, less than or equal to 0.010% of N, less than or equal to 0.030% of Al, 1.45% -1.75% of W, 0.002% -0.006% of B, 0.010% -0.060% of Ti, less than or equal to 0.40% of Ni, and the balance of Fe and unavoidable impurities.
2. The method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat resistant alloy seamless steel pipe according to claim 1, wherein in the tempering pretreatment process, the soaking time is 3min/mm.
3. The method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe according to claim 1, wherein in the normalizing process, the normalizing holding temperature is 1040-1180 ℃ and the soaking time is 1.5min/mm.
4. The method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat resistant alloy seamless steel pipe according to claim 1, wherein in the normalizing process, a rapid cooling process is performed to 400 ℃ or lower.
5. The method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat resistant alloy seamless steel pipe according to claim 4, wherein, in the normalizing process,
the rapid cooling treatment is carried out to room temperature;
and/or the rapid cooling treatment adopts water cooling, a water mist cooling area or air cooling.
6. The method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe according to claim 1, wherein in the tempering heat treatment process, the tempering heat preservation temperature is 730 ℃ to 800 ℃ and the soaking time is 2.5min/mm.
7. The method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat resistant alloy seamless steel pipe according to claim 1, wherein a rapid cooling process is performed in the tempering heat treatment process.
8. The method for improving the impact toughness of a 2.25Cr-1.6W-V-Nb heat-resistant alloy seamless steel pipe according to any one of claims 1 to 7, wherein the outer diameter of the seamless steel pipe is 51mm to 800mm and the wall thickness is 4.5mm to 150mm.
9. A seamless steel tube of a 2.25Cr-1.6W-V-Nb heat resistant alloy, characterized in that the seamless steel tube is produced by the method of any one of claims 1 to 8.
10. The seamless steel tube of a 2.25Cr-1.6W-V-Nb heat resistant alloy according to claim 9 wherein the seamless steel tube has a yield strength of not less than 400MPa, a tensile strength of not less than 510MPa, an elongation after break of not less than 20%, and an impact absorption work of not less than 40J.
11. Use of a 2.25Cr-1.6W-V-Nb heat resistant alloy steel pipe according to claim 10 in a ultra supercritical power generation unit as an alloy pipe for steam pipelines, header components, water walls.
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