Alloy steel pipe and manufacturing process thereof

Abstract

The invention relates to the field of alloy, and particularly discloses an alloy steel pipe and a manufacturing process thereof, the alloy steel pipe comprises the following raw materials: 0.08%-0.11% of C, 0.23%-0.3% of Si, 0.4%-0.55% of Mn, 8.7%-9.2% of Cr, 0.35%-0.5% of Mo, 1.6%-1.9% of W, 0.15%-0.22% of V, 0.06%-0.075% of Nb, 0.016%-0.018% of B, 0.045%-0.06% of N, 0.001%-0.006% of Al, 0.2%-0.4% of Ni, 0.03%-0.035% of other elements and the balance of iron; the manufacturing process comprises the following steps: uniformly mixing the raw materials, and carrying out vacuum melting treatment, cooling and ingot casting, hot rolling and perforating treatment, normalizing, tempering treatment, cold drawing and annealing to obtain a finished product. And the high-temperature strength durability is good, the structure uniformity is high, and the content of harmful elements is low.

Description

Technical Field

[0001] This application relates to the field of alloys, and more specifically, to an alloy steel pipe and its manufacturing process. Background Technology

[0002] Existing alloy steel pipes typically use P92 steel, a key material for supercritical thermal power units. However, it has some issues with high-temperature strength, creep resistance, and weldability, directly affecting the safe service life of boiler tubes. For example, its high-temperature creep strength is insufficient. The national standard GB / T5310-2017 requires a creep strength of ≥85MPa at 625℃ / 100,000 hours, but in actual applications, some P92 steel pipes can only reach 80-90MPa, making them prone to creep failure after long-term operation. There is also the problem of uneven microstructure. P92 steel pipes produced by traditional processes have large differences in grain size along the wall thickness direction (generally grade 4-7) and are prone to the formation of δ-ferrite, reducing their high-temperature performance. There is also the influence of harmful elements, such as As and Sn, which tend to segregate at grain boundaries, accelerating high-temperature embrittlement.

[0003] Therefore, the question is how to prepare a new type of alloy steel pipe that has the advantages of good high-temperature strength retention, high microstructure uniformity, and low content of harmful elements, thereby improving the service performance of alloy steel pipes. Summary of the Invention

[0004] In order to prepare a new alloy steel pipe with advantages such as good high-temperature strength retention, high microstructure uniformity and low content of harmful elements, this application provides an alloy steel pipe and its manufacturing process.

[0005] In a first aspect, this application provides an alloy steel pipe, which adopts the following technical solution: An alloy steel pipe comprising the following raw materials by weight percentage: C: 0.08-0.11%, Si: 0.23-0.3%, Mn: 0.4-0.55%, Cr: 8.7-9.2%, Mo: 0.35-0.5%, W: 1.6-1.9%, V: 0.15-0.22%, Nb: 0.06-0.075%, B: 0.016-0.018%, N: 0.045-0.06%, Al: 0.001-0.006%, Ni: 0.2-0.4%, other elements 0.03-0.035%, and the balance being iron.

[0006] By employing the above technical solutions, chromium (Cr) and molybdenum (Mo) are dissolved in the iron matrix, significantly improving high-temperature creep resistance; a dense chromium oxide layer can be formed when the Cr content is 8.7-9.2%, enhancing oxidation resistance and delaying high-temperature failure; Mo in the range of 0.35-0.5% suppresses temper brittleness, improving high-temperature hardness and creep strength; and vanadium (V) and niobium (Nb) form fine carbonitride particles, such as VC and NbC, which utilize their pinned dislocation structure to hinder grain boundary slip; a V content of 0.15-0.22% and an Nb content of 0.06%... The -0.075% synergistic effect improves creep resistance, significantly reducing the deformation rate of the steel pipe at high temperatures. Simultaneously, the limited boron (B) content enhances grain boundary bonding, preventing the propagation of intergranular cracks at high temperatures, while the 1.6-1.9% tungsten (W) content further enhances thermal strength through solid solution strengthening, synergistically extending service life with Mo. This gives the alloy steel pipe the advantage of good strength preservation at high temperatures. Under a service environment of 625℃ / 100,000 hours, the creep strength of the heat-resistant alloy steel pipe reaches ≥95MPa, significantly improving the durability of the steel pipe and extending its service life.

[0007] The carbon (C) content is controlled at a low level of 0.08-0.11% to avoid carbide coarsening and ensure microstructure stability. Silicon (Si) content of 0.25-0.3% and aluminum (Al) content of 0.001-0.006% act as deoxidizers, reducing non-metallic inclusions and improving the purity of the molten steel, thereby refining grain size and improving the microstructure uniformity of the alloy steel pipe. Nitrogen (N) content of 0.045-0.06% combines with vanadium and niobium to form fine nitrides, such as VN, which, by inhibiting grain growth and utilizing the filling effect of fine grains, improves the uniformity and density of the microstructure. Simultaneously, nickel (Ni) content of 0.2-0.4% can stabilize the microstructure, reduce phase transformation stress, and further control the microporosity within the microstructure, thereby further improving the internal microstructure uniformity of the alloy steel pipe.

[0008] The total amount of harmful elements such as phosphorus (P) and sulfur (S) is limited to within 0.03%-0.035% to avoid the formation of harmful inclusions, thereby reducing grain boundary brittleness and corrosion sensitivity, and improving toughness and high-temperature durability. The manganese (Mn) content of 0.4-0.55% reduces the harm of sulfur by forming MnS to encapsulate sulfur impurities. At the same time, the addition of chromium (Cr) and molybdenum (Mo) further inhibits impurity segregation, ensures the purity of the microstructure, and reduces the risk of oxidation and corrosion. As a result, alloy steel pipes have the advantages of good high-temperature strength preservation, high microstructure uniformity, and low content of harmful elements.

[0009] Preferably, the other elements include Pb: 0.004, Bi: 0.007, Sn: 0.005, As: 0.008, and Sb: 0.01.

[0010] By adopting the above technical solutions, Sn, Sb, and As segregate along grain boundaries at high temperatures, forming low-melting-point liquid phases, which weaken grain boundary bonding forces, accelerate the initiation and propagation of high-temperature creep cracks, and lead to a decrease in creep strength of more than 30%. Bi forms a low-melting-point eutectic phase with the iron matrix, which induces grain boundary liquefaction when in service above 600°C, significantly reducing creep resistance and thus improving the strength and durability at high temperatures. Pb is dispersed in the matrix in the form of nano-sized particles, which become channels for dislocation slip under high-temperature stress, accelerating the plastic deformation process and shortening the creep fracture time. Sb promotes carbide coarsening, weakens the precipitation strengthening effect, and further improves the strength and durability of alloy steel pipes at high temperatures.

[0011] Controlling the upper limit of harmful elements can prevent multiple deteriorations caused by cumulative effects. When Sn > 0.005%, the high-temperature ductility of steel decreases sharply; when As > 0.01%, it will significantly increase the sensitivity to temper brittleness and reduce the content of harmful elements in alloy steel pipes.

[0012] Preferably, the V / Nb ratio is 2.7-3.2.

[0013] By adopting the above technical solution, when V / Nb = 2.7–3.2, the ratio of V-dominant MC-type carbides to Nb-dominant NbC is balanced, improving high-temperature creep strength; Nb inhibits the excessive growth of V carbides at temperatures above 600℃, maintains the stability of the precipitate phase, and prolongs the creep rupture time, thereby further improving the strength and durability of alloy steel pipes under high-temperature conditions.

[0014] When V / Nb is greater than 3.2, excess V leads to the segregation of interdendritic carbides; when V / Nb is less than 2.7, excess Nb may form coarse Laves phase; a ratio of 2.7–3.2 gives the alloy steel pipe better microstructure uniformity.

[0015] Secondly, this application provides a manufacturing process for alloy steel pipes, employing the following technical solution: A manufacturing process for an alloy steel pipe includes the following steps: S1. Mix all raw materials evenly to obtain a mixture; the mixture is then vacuum melted, cooled, and cast into an ingot to obtain a billet; S2. The billet is heated to 1170-1190℃ and then hot-rolled and pierced. After hot rolling and piercing, a semi-finished product is obtained. S3. The semi-finished product undergoes dual heat treatment of normalizing and tempering, and finally cold drawing and annealing to obtain the finished product.

[0016] By adopting the above technical solution, the raw material mixing and smelting results in uniform distribution of raw materials. After smelting, the ingot is cooled and cast to obtain a uniformly mixed billet. During the smelting process, the vacuum conditions can promote the preferential volatilization and removal of low-boiling-point impurities such as Pb, Bi, and Sn, thereby reducing the impurity content. At the same time, it can inhibit the dissolution of gaseous impurities such as oxygen and hydrogen, reduce oxide inclusions, improve the purity of the body, and ensure the internal uniformity of the alloy steel pipe. At the same time, the high-density alloy steel pipe has good high-temperature resistance and durability.

[0017] Hot rolling piercing is performed at 1170–1190℃ to trigger complete austenite recrystallization, homogenize the grain size to ASTM 6–8 grade, and break up coarse carbides when the piercing deformation is greater than 70%, avoiding chain segregation and refining the grains, thereby improving the high-temperature strength durability and microstructure uniformity of the alloy steel pipe.

[0018] Under the dual heat treatment conditions of normalizing and tempering, the semi-finished product can completely recrystallize and eliminate the rolling texture. Furthermore, as the tempered strands disperse and precipitate carbides from the transverse grains, they prevent the migration of high-temperature grain boundaries, further improving the high-temperature strength and durability of the alloy steel pipe. Cold drawing and annealing can further stabilize the grain boundaries, control the generation of impurities, and improve the uniformity and purity of the alloy steel pipe's microstructure.

[0019] Preferably, the vacuum degree of the vacuum melting process in S1 is 0.005-0.01 Pa, the melting temperature is 1535-1570℃, the time is 30-50 min, and the heating rate is 5-10℃ / min.

[0020] By adopting the above technical solution, ultra-high vacuum (0.005–0.01 Pa) promotes the efficient volatilization and removal of low-boiling-point impurities such as Pb, Bi, and Sn, with a residual total of ≤0.01%, significantly reducing the risk of high-temperature grain boundary embrittlement, decreasing the dissolution rate of gaseous impurities such as oxygen and hydrogen, reducing oxide inclusions, improving matrix continuity, and enhancing the strength and durability of alloy steel pipes under high-temperature conditions.

[0021] High-temperature melting at 1535–1570℃ fully dissolves V / Nb carbonitrides, avoiding unmelted phase residue; combined with 30–50 min of heat preservation, it ensures uniform diffusion of microalloying elements (V, Nb) to form ultrafine precipitated strengthening phases; slow heating at 5–10℃ / min inhibits the volatilization of elements such as Mn and Cr, and by controlling the proportion of alloying elements, the strength and durability of alloy steel pipes under high-temperature conditions are further improved.

[0022] The ultra-high vacuum environment blocks atmospheric pollution, and the slow heating reduces the width of the dendritic segregation zone, resulting in extremely low fluctuations in the composition of the ingot. Combined with a melting temperature of >1535℃, it thoroughly decomposes coarse primary carbides and eliminates local enrichment defects, ensuring that the alloy steel pipe has a high degree of structural uniformity.

[0023] Preferably, the holding time for the hot rolling piercing treatment is 2-2.5 hours, and the final rolling temperature is 950-1000℃.

[0024] By adopting the above technical solution, the final rolling temperature of 950–1000℃ is higher than the lower limit of the dynamic recrystallization temperature of austenite (usually ≥900℃), triggering complete recrystallization and forming fine equiaxed austenite grains, which significantly improves the high-temperature creep resistance. High-temperature heat preservation promotes the full solid solution of V / Nb carbonitrides, and nanoscale dispersed phases (such as VC and NbC) precipitate during the cooling process, effectively pinning dislocations, inhibiting high-temperature grain boundary slip, and prolonging the creep fracture time, thereby improving the strength and durability of alloy steel pipes under high-temperature conditions.

[0025] The final rolling temperature of 950–1000℃ avoids abnormal grain growth, forms uniform equiaxed ferrite grains, increases the grain boundary area, and reduces stress concentration; the holding stage promotes the decomposition of pearlite-ferrite bands, and the post-rolling cooling rate control inhibits the regeneration of banded structures, thereby improving the uniformity of the internal microstructure of the alloy steel pipe.

[0026] Preferably, the normalizing treatment is performed at a temperature of 1060-1080℃ for 1-1.5 hours, followed by natural air cooling to room temperature.

[0027] Preferably, the tempering treatment is performed at a temperature of 760-780℃ for 2-2.5 hours, followed by natural air cooling to room temperature.

[0028] By adopting the above technical solution, 1060–1080℃ can completely dissolve V / Nb carbonitrides and eliminate the segregation of chain carbides left over from hot rolling; while 1–1.5h of heat preservation ensures the homogenization of austenite composition, and high-temperature normalizing triggers secondary recrystallization, refining the crystals, thereby improving the microstructure uniformity of alloy steel pipes.

[0029] Tempering at 760–780℃ promotes the dispersed precipitation of V / Nb carbides and inhibits the coarsening of the precipitated phase. Holding at 2–2.5h ensures the full diffusion of Mo / W solid solution atoms, strengthens the anti-slip ability of grain boundaries, and improves the strength and durability of alloy steel pipes under high temperature conditions.

[0030] Preferably, the cold drawing deformation is 10-14%, the annealing temperature is 640-660℃, and the annealing time is 1-1.5h.

[0031] By adopting the above technical solution, cold drawing deformation forms an entangled dislocation network inside the alloy steel pipe, which significantly improves the room temperature yield strength and provides a basic dislocation structure for subsequent high-temperature pinning. In addition, cold drawing can compress the long axis of the grains, improve the axial creep resistance at high temperatures, and thus improve the strength durability of the alloy steel pipe under high-temperature conditions.

[0032] Annealing at 640–660℃ triggers polygonization, dislocation rearrangement forms subgrain boundaries, eliminates residual stress from cold drawing, and inhibits high-temperature stress concentration cracking. Holding at 1–1.5h ensures sufficient coarsening of subgrains and avoids mixed crystals caused by rapid recrystallization, thereby improving the microstructure uniformity and high-temperature strength durability of alloy steel pipes.

[0033] In summary, this application has the following beneficial effects: 1. Under service conditions of 625℃ / 100,000 hours, the endurance strength of the heat-resistant alloy steel pipe reaches ≥95MPa, which significantly improves the durability of the steel pipe, extends its service life, and solves the problem of steel pipes being easily eroded and damaged by liquid lead (lead bismuth) in the existing technology.

[0034] 2. By optimizing the C content (0.08-0.11%) and adopting a dual heat treatment process, including normalizing at 1070℃±10℃ and tempering at 770℃±10℃, the steel pipe has excellent plasticity and toughness, avoiding the problem of brittleness in traditional P92 steel at high temperatures.

[0035] 3. By precisely controlling the tempering temperature (770℃±10℃) and time (2h), the uniform precipitation of M23C6 and MX phases is ensured, eliminating δ ferrite in the metallographic structure, preventing it from becoming the origin of creep cracks, and significantly improving the long-term strength of the steel pipe.

[0036] 4. The vacuum induction melting process effectively reduces the content of oxide inclusions and improves the purity of the steel pipe, thereby further enhancing the corrosion resistance and service life of the steel pipe.

[0037] 5. By controlling the amount of cold drawing deformation (10-15%), appropriate dislocation strengthening is introduced, the microstructure is optimized, the creep resistance and fatigue life of the steel pipe are improved, and the problem of easy creep of steel pipe in high temperature environment in the existing technology is effectively solved.

[0038] 6. W / B / N synergistic control: W content is slightly lower than the traditional upper limit to avoid hot working cracks; the ratio of B to N is optimized to prevent grain boundary precipitates.

[0039] 7. V / Nb ratio: V / Nb = 2.7-3.2, which promotes the precipitation of fine MX (Nb%, V) (C%, N) and improves creep resistance.

[0040] 8. The addition of Ni can lower the γ→α phase transformation temperature and avoid the formation of δ ferrite (harmful phase) at high temperatures. When the Ni content is ≥0.2%, δ ferrite can be completely suppressed during the normalizing cooling process of alloy steel pipe. Attached Figure Description

[0041] Figure 1 This refers to the room temperature yield strength of the alloy steel pipe tested in this application; Figure 2 This refers to the room temperature tensile strength of the alloy steel pipe tested in this application; Figure 3 This refers to the room temperature elongation after fracture of the alloy steel pipe tested in this application; Figure 4 This refers to the room temperature impact energy of the alloy steel pipe tested in this application; Figure 5 Metallographic image (500×) of the outer wall of the alloy steel pipe sample from Example 1 of this application; Figure 6 This is a metallographic photograph (500×) of the wall of the alloy steel pipe sample of Example 1 of this application; Figure 7 This is a metallographic photograph (500×) of the inner wall of the alloy steel pipe sample of Example 1 of this application; Figure 8 This is a metallographic photograph (500×) of the outer wall of the alloy steel pipe sample of Example 2 of this application; Figure 9 This is a metallographic photograph (500×) of the tube wall of Example 2 of the alloy steel pipe of this application; Figure 10 This is a metallographic photograph (500×) of the inner wall of the alloy steel pipe sample of Example 2 of this application. Detailed Implementation

[0042] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. Example

[0043] Example 1: An alloy steel pipe; C: 0.082%, Si: 0.25%, Mn: 0.47%, Cr: 8.70%, Mo: 0.38%, W: 1.72%, V: 0.17%, Nb: 0.061%, B: 0.018%, N: 0.054%, Al: 0.004%, Ni: 0.2%, other elements 0.034%, balance made up to 100% with iron; other elements include Pb: 0.004%, Bi: 0.007%, Sn: 0.005%, As: 0.008%, Sb: 0.01%. The manufacturing process is as follows: S1. Mix all raw materials evenly to obtain a mixture; the mixture is vacuum melted under the conditions of vacuum degree 0.008Pa, melting temperature 1555℃, time 40min, and heating rate 8℃ / min, and then cooled and cast into an ingot to obtain a billet; S2. The billet is heated to 1180℃ and hot-rolled and pierced. The holding time is 2 hours and the final rolling temperature is 980℃. After hot rolling and piercing, it is naturally air-cooled to room temperature to obtain a semi-finished product. S3. The semi-finished product is heated to 1070℃ at a heating rate of 5℃ / min for normalizing treatment for 1 hour, and then naturally cooled to room temperature. The product is then heated to 770℃ at a heating rate of 5℃ / min for tempering treatment for 2 hours, and then naturally cooled to room temperature to complete the double heat treatment. Finally, it is cold drawn and annealed with a cold drawing deformation of 12% and an annealing temperature of 650℃ for 1 hour, and then naturally cooled to room temperature to obtain the finished product.

[0044] Example 2: The difference between this example and Example 1 is that; C: 0.080%, Si: 0.23%, Mn: 0.47%, Cr: 8.90%, Mo: 0.41%, W: 1.67%, V: 0.19%, Nb: 0.063%, B: 0.016%, N: 0.054%, Al: 0.0017%, Ni: 0.24%, other elements 0.03%, balance made up to 100% with iron; other elements include pb: 0.004%, Bi: 0.006%, Sn: 0.003%, As: 0.007%, Sb: 0.01%.

[0045] Example 3: The difference between this example and Example 1 is that: C: 0.08%, Si: 0.23%, Mn: 0.4%, Cr: 8.7%, Mo: 0.35%, W: 1.6%, V: 0.15%, Nb: 0.06%, B: 0.016%, N: 0.045%, Al: 0.001%, Ni: 0.2%, other elements 0.03%, balance made up to 100% with iron; other elements include Pb: 0.004%, Bi: 0.006%, Sn: 0.003%, As: 0.007%, Sb: 0.01%. The manufacturing process is as follows: S1. Mix all raw materials evenly to obtain a mixture; the mixture is vacuum melted under the conditions of vacuum degree 0.005Pa, melting temperature 1535℃, time 50min, and heating rate 5℃ / min, and then cooled and cast into an ingot to obtain a billet; S2. The billet is heated to 1170℃ and hot-rolled and pierced. The holding time is 2.5h and the final rolling temperature is 950℃. After hot rolling and piercing, it is naturally air-cooled to room temperature to obtain a semi-finished product. S3. The semi-finished product is heated to 1060℃ at a heating rate of 5℃ / min for normalizing treatment for 1.5 hours, and then naturally cooled to room temperature. The product is then heated to 760℃ at a heating rate of 5℃ / min for tempering treatment for 2.5 hours, and then naturally cooled to room temperature, completing the double heat treatment. Finally, it undergoes cold drawing and annealing with a cold drawing deformation of 10% and an annealing temperature of 640℃ for 1.5 hours, followed by natural air cooling to room temperature to obtain the finished product.

[0046] Example 4: The difference between this example and Example 1 is that: C: 0.11%, Si: 0.3%, Mn: 0.55%, Cr: 9.2%, Mo: 0.5%, W: 1.9%, V: 0.22%, Nb: 0.075%, B: 0.018%, N: 0.06%, Al: 0.006%, Ni: 0.4%, other elements 0.035%, balance made up to 100% with iron; other elements include Pb: 0.005%, Bi: 0.007%, Sn: 0.004%, As: 0.008%, Sb: 0.011%. The manufacturing process is as follows: S1. Mix all raw materials evenly to obtain a mixture; the mixture is vacuum melted under the conditions of vacuum degree 0.01Pa, melting temperature 1570℃, time 30min, and heating rate 10℃ / min, and then cooled and cast into an ingot to obtain a billet; S2. The billet is heated to 1190℃ and hot-rolled and pierced. The holding time is 2 hours and the final rolling temperature is 1000℃. After hot rolling and piercing, it is naturally air-cooled to room temperature to obtain a semi-finished product. S3. The semi-finished product is heated to 1080℃ at a heating rate of 5℃ / min for normalizing treatment for 1 hour, and then naturally cooled to room temperature. The semi-finished product is then heated to 780℃ at a heating rate of 5℃ / min for tempering treatment for 2 hours, and then naturally cooled to room temperature to complete the double heat treatment. Finally, it is cold drawn and annealed with a cold drawing deformation of 12% and an annealing temperature of 660℃ for 1 hour, and then naturally cooled to room temperature to obtain the finished product.

[0047] Example 5: The difference between this example and Example 2 is that: V is 0.189%, Nb is 0.07%, and V / Nb = 2.7.

[0048] Example 6: The difference between this example and Example 2 is that: V is 0.208%, Nb is 0.065%, and V / Nb = 3.2.

[0049] Comparative Example Comparative Example 1: The difference between this comparative example and Example 1 is that: C:0.07%, Si:0.35%, Mn0.6%, Cr:8.90%, Mo:0.57%, W:1.50%, V:0.25%, Nb:0.058%, B:0.045%, N :0.030%, Al: 0.0010%, V / Nb=4.31%, pb: 0.006%, Bi: 0.010%, Sn: 0.006%, As: 0.008%, Sb: 0.02.

[0050] Comparative Example 2: This comparative example differs from Example 1 in that: C:0.07%, Si:0.35%, Mn0.6%, Cr:8.90%, Mo:0.57%, W:1.50%, V:0.23%, Nb:0.048%, B:0.045%, N: 0.030%, Al: 0.0010%, V / Nb=4.79%, pb: 0.008%, Bi: 0.006%, Sn: 0.005%, As: 0.01%, Sb: 0.01.

[0051] Performance testing 1. Tensile test at room temperature Alloy steel pipes were prepared using the methods of Examples 1-6 and Comparative Examples 1-2, respectively. The yield strength, tensile strength, elongation after fracture, and reduction of area were tested and recorded in accordance with GB / T228.1.

[0052] Table 1 Tensile Property Test Table ("-" in the table indicates that this item was not tested in the example and there is no data) 2. Room temperature shock test Alloy steel pipes were prepared using the methods of Examples 1-2 and Comparative Examples 1-2, respectively. Impact energy was tested according to GB / T229, and data were recorded.

[0053] Table 2 Performance Test Table 3. Bending test Alloy steel pipes were prepared using the methods of Examples 1-2, and their bending properties were tested according to GB / T244, with data recorded.

[0054] Table 3 Performance Test Table 5. Metallographic test Alloy steel pipes were prepared using the methods of Examples 1-2, and their crystal phase diagrams were observed under a microscope. Table 4 Test Table Combined with Table 1-4 and Figure 1-10 It can be seen that the alloy steel pipe prepared in this application has high strength and high microstructure uniformity; W / B / N synergistic control: the W content is slightly lower than the traditional upper limit to avoid hot working cracks; the ratio of B to N optimizes the grain boundary precipitates; V / Nb ratio: V / Nb=2.7-3.2, promotes the precipitation of fine MX(Nb,V)(C,N) and improves creep resistance.

[0055] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. An alloy steel pipe, characterized in that, The raw materials contain the following weight percentages: C: 0.08-0.11%, Si: 0.23-0.3%, Mn: 0.4-0.55%, Cr: 8.7-9.2%, Mo: 0.35-0.5%, W: 1.6-1.9%, V: 0.15-0.22%, Nb: 0.06-0.075%, B: 0.016-0.018%, N: 0.045-0.06%, Al: 0.001-0.006%, Ni: 0.2-0.4%, other elements 0.03-0.035%, and the balance is iron.

2. The alloy steel pipe according to claim 1, characterized in that: The other elements include Pb: 0.004, Bi: 0.007, Sn: 0.005, As: 0.008, and Sb: 0.

01.

3. The alloy steel pipe according to claim 1, characterized in that, The V / Nb ratio is 2.7-3.

2.

4. The manufacturing process of an alloy steel pipe according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Mix all raw materials evenly to obtain a mixture; the mixture is then vacuum melted, cooled, and cast into an ingot to obtain a billet; S2. The billet is heated to 1170-1190℃ and then hot-rolled and pierced. After hot rolling and piercing, a semi-finished product is obtained. S3. The semi-finished product undergoes dual heat treatment of normalizing and tempering, and finally cold drawing and annealing to obtain the finished product.

5. The manufacturing process of an alloy steel pipe according to claim 4, characterized in that, The vacuum degree of the vacuum melting process in S1 is 0.005-0.01 Pa, the melting temperature is 1535-1570℃, the time is 30-50 min, and the heating rate is 5-10℃ / min.

6. The manufacturing process of an alloy steel pipe according to claim 4, characterized in that, The holding time for the hot rolling piercing treatment is 2-2.5 hours, and the final rolling temperature is 950-1000℃.

7. The manufacturing process of an alloy steel pipe according to claim 4, characterized in that, The normalizing treatment is performed at a temperature of 1060-1080℃ for 1-1.5 hours, followed by natural air cooling to room temperature.

8. The manufacturing process of an alloy steel pipe according to claim 4, characterized in that, The tempering treatment is performed at a temperature of 760-780℃ for 2-2.5 hours, followed by natural air cooling to room temperature.

9. The manufacturing process of an alloy steel pipe according to claim 4, characterized in that, The cold drawing deformation is 10-14%, the annealing temperature is 640-660℃, and the time is 1-1.5h.

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