A coarse equiaxed grain structure n08120 nickel-based alloy seamless pipe and a preparation method thereof

Abstract

The present application belongs to the technical field of nickel-based alloy seamless pipe and its manufacturing technology, and particularly relates to a coarse equiaxed crystal structure N08120 nickel-based alloy seamless pipe and a preparation method thereof. By controlling the content of carbon, chromium, nickel and niobium and the like in the N08120 nickel-based alloy, and the cold rolling deformation and the heat treatment temperature, the formation and uniform distribution of the coarse equiaxed crystal structure in the nickel-based alloy seamless pipe are ensured, and the performance of the N08120 nickel-based alloy seamless pipe is not adversely affected. The preparation method of the N08120 nickel-based alloy seamless pipe provided by the present application realizes the requirement of the nickel-based alloy seamless pipe having the coarse equiaxed crystal structure, and the prepared seamless pipe has good high-temperature stability, corrosion resistance and mechanical properties, high size precision and good surface quality, and can be used in the structural material field of various specifications of furnace pipes, heating pipes and hot storage devices and the like, improves the stability and corrosion resistance of the structural material, and has important significance for actual production.

Description

Technical Field

[0001] This invention belongs to the field of nickel-based alloy seamless tubes and their manufacturing technology, specifically relating to a coarse equiaxed grain structure N08120 nickel-based alloy seamless tube and its preparation method. Background Technology

[0002] High-temperature alloys generally refer to alloy materials that can withstand large and complex stresses at temperatures above 600°C and possess a certain degree of surface stability. They are typically iron-based, nickel-based, and cobalt-based. High-temperature alloys exhibit good high-temperature tensile strength, oxidation and corrosion resistance, fatigue resistance, creep resistance, fracture resistance, and structural stability. Based on their strengthening type, high-temperature alloys can be classified into solid solution-strengthened high-temperature alloys and precipitation-strengthened high-temperature alloys.

[0003] N08120 is a Fe-Ni based alloy developed by Hastelloy, a typical solid solution strengthened nickel-based heat-resistant alloy. Due to its excellent high-temperature strength and corrosion resistance, it is widely used in heat treatment furnace bodies and heating tubes, among other high-temperature and corrosion-resistant materials. Cr, Mo, Fe, and Nb are representative solid solution strengthening elements in N08120 nickel-based alloys. Cr and Mo improve the alloy's corrosion resistance, Fe reduces costs, and Nb promotes precipitation hardening. Because N08120 alloy contains a high amount of carbon and many easily precipitated elements (such as chromium, molybdenum, and niobium), it easily forms precipitate phases. When used in complex high-temperature environments, the microstructure of N08120 alloy is highly likely to change, thus affecting the stability of N08120 alloy castings during use. The stability of the alloy in high-temperature environments depends on the uniformity of the coarse equiaxed grain structure. When the equiaxed grain size reaches level 5 or coarser, the stability of N08120 alloy in complex high-temperature environments is better.

[0004] Patent application number 201710887663.3 discloses a method for manufacturing large-diameter seamless tubes of UNS N08810 iron-nickel-based alloy for high-temperature heating furnaces. The method includes the following steps: first, directly casting a square ingot that meets the requirements using electric arc smelting; then, blanking the square ingot; next, producing a rough tube using hot piercing; and finally, controlling the uniformity of the tube's microstructure through cold working and a matching heat treatment process, supplemented by a tube surface treatment process, resulting in high performance and high surface quality. The tube's microstructure is equiaxed crystal with a grain size of 3-5. The room temperature tensile properties of the finished tube are: tensile strength ≥ 500 MPa, yield strength ≥ 210 MPa, elongation ≥ 50%; the tensile properties at 650℃ are: tensile strength ≥ 400 MPa, yield strength ≥ 120 MPa, elongation ≥ 50%. The above manufacturing method is only applicable to the preparation of large-diameter seamless tubes of UNS N08810 iron-nickel-based alloy, and is not universally applicable to seamless tubes of N08120 alloy that have higher stability requirements in high-temperature and complex environments. Summary of the Invention

[0005] In actual production, N08120 nickel-based alloy seamless tubes are usually subjected to solution heat treatment. Due to the high carbon content and the presence of other easily precipitated elements in this alloy, improper solution heat treatment can lead to the formation of carbide precipitates at the grain boundaries, affecting the alloy's performance. The stability of the alloy at high temperatures depends on the uniformity of the grain size, which is affected by both the amount of deformation and the solution heat treatment process.

[0006] Therefore, in order to solve the problem that it is difficult to simultaneously and accurately control the formation of coarse equiaxed grain structure and improve corrosion resistance in existing N08120 nickel-based alloy seamless tubes, the purpose of this invention is to provide a coarse equiaxed grain structure N08120 nickel-based alloy seamless tube and its preparation method. By studying the composition, deformation amount and solution heat treatment temperature of N08120 nickel-based alloy seamless tube, the requirement of coarse equiaxed grain structure of N08120 nickel-based alloy seamless tube is achieved, ensuring its high-temperature performance. It can be used in the field of structural materials such as furnace tubes, heating tubes and heat storage devices of various specifications.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing a seamless N08120 nickel-based alloy tube with a coarse equiaxed grain structure includes the following steps:

[0009] S1. Refining and electroslag remelting are carried out in an electric arc furnace, followed by hot forging to obtain N08120 nickel-based alloy round steel.

[0010] As a preferred embodiment of the above technical solution, in step S1, the composition and weight percentage of the N08120 nickel-based alloy round steel are as follows: 0.05%≤C≤0.10%; Si≤1.0%; Mn≤1.5%; S≤0.03%; 36.0%≤Ni≤39.0%; Cu≤0.50%; Mo≤2.50%; 25.0%≤Cr≤27.0%; Al≤0.40%; Ti≤0.20%; P≤0.04%; B≤0.010%; Co≤3.0%; 0.45%≤Nb≤0.9%; W≤2.5%; 0.15%≤N≤0.30%; Fe = balance.

[0011] In the above technical solution, by controlling the content of carbon, chromium, nickel, and niobium in the N08120 nickel-based alloy, good corrosion resistance can be provided for the seamless nickel-based alloy tube. Specifically, this invention controls the lower limit of the carbon content in the nickel-based alloy to above 0.05%, ensuring the alloy's high-temperature strength, and the upper limit to ensure its corrosion resistance. Therefore, selecting a carbon content between 0.05% and 0.10% effectively improves the high-temperature performance of the N08120 nickel-based alloy seamless tube. Controlling the content of chromium, nickel, and niobium at the standard upper limit ensures the overall performance of the alloy.

[0012] As a preferred embodiment of the above technical solution, in step S1, the forging ratio of the hot forging process is not less than 4.0. The present invention sets the forging ratio to be not less than 4.0 during the hot forging process primarily because when the forging ratio is greater than or equal to 4.0, the elemental distribution within the nickel-based alloy becomes more uniform, allowing carbides to more easily form dispersed fine reinforcing phases, thereby improving the corrosion resistance and mechanical properties of the nickel-based alloy. Conversely, when the forging ratio is less than 4.0, the distribution of elements in the alloy becomes uneven, leading to varying degrees of decline in both corrosion resistance and mechanical properties.

[0013] S2. Cut the round steel in step S1 into short pieces, then drill holes, chamfer, and clean the short pieces. Then heat them in a primary induction heating furnace, expand the holes, heat them in a secondary induction heating furnace, and finally perform hot extrusion to obtain a rough tube.

[0014] As a preferred embodiment of the above technical solution, step S2 further includes preheating the cleaned short material to 900-1000°C for 1-2 hours before heating in the induction heating furnace. Preheating softens the billet, improves its plasticity, and reduces the requirements for molds and equipment; moreover, if the preheating temperature is not within the range of 900-1000°C, hot extrusion is difficult to perform and may cause stalling.

[0015] As a preferred embodiment of the above technical solution, in step S2, the heating temperature of the primary induction heating furnace < the heating temperature of the secondary induction heating furnace = the extrusion temperature of the hot extrusion.

[0016] As a preferred embodiment of the above technical solution, in step S2, the extrusion temperature of the hot extrusion treatment is 1180-1250℃, and the extrusion ratio is 15-20.

[0017] In the above technical solution, the extrusion temperature of the hot extrusion treatment is 1180-1250℃. Within this temperature range, the deformation resistance of the billet is small and it is easy to undergo plastic deformation. At the same time, a larger extrusion ratio (15-20) can cause severe initial grain breakage and sufficient grain refinement. When the extrusion ratio is less than 15, the grain size is large and the uniformity is poor, which easily leads to the formation of mixed crystal structure. When the extrusion ratio is greater than 20, the grain size is significantly refined, but the internal forces of the material are large, which easily leads to microcracks and may also produce carbide precipitates, which are not conducive to subsequent processing.

[0018] As a preferred embodiment of the above technical solution, the rough pipe obtained in step S2 still needs to undergo finishing treatment.

[0019] S3. The rough tube from step S2 is cold rolled into a tube of the required specifications.

[0020] As a preferred embodiment of the above technical solution, during the cold rolling process in step S3, the deformation amount in a single step is at least ≥50%; the purpose is to achieve greater deformation of the extruded rough tube, which can refine and homogenize the grains and improve product production efficiency.

[0021] The amount of deformation can alter the microstructure of an alloy to a certain extent. In the above-mentioned technical solutions, selecting a single deformation amount of at least 50% or more can effectively break down the microstructure, resulting in better anisotropy of grains within the microstructure. This allows for better achievement of anisotropy during subsequent heat treatment, which is a prerequisite for ensuring that the material has an equiaxed grain structure.

[0022] As a preferred embodiment of the above technical solution, in the cold rolling process of step S2, if it is a multi-pass cold rolling process, the pipe needs to be degreased, heat treated, pickled and straightened in sequence after each pass of cold rolling.

[0023] S4. The tube from step S3 is sequentially subjected to degreasing, heat treatment, pickling, straightening, and polishing. After finishing, a coarse equiaxed crystal structure N08120 nickel-based alloy seamless tube is obtained.

[0024] As a preferred embodiment of the above technical solution, in step S4, the temperature of the heat treatment is 1190–1250°C.

[0025] In the above technical solution, the heat treatment temperature is set within the range of 1190–1250℃, which allows for the stable formation of coarse equiaxed grains in the nickel-based alloy. Higher heat treatment temperatures result in larger grain sizes and more stable high-temperature performance of the material. Furthermore, due to the high temperature and high degree of material softening, defects such as bending and cracking are less likely to occur in the tube during multi-pass cold rolling.

[0026] In summary, the present invention has the following beneficial effects:

[0027] 1. This invention ensures the formation and uniform distribution of coarse equiaxed grain structure in nickel-based alloy seamless tubes by controlling the content of elements such as carbon, chromium, nickel and niobium in N08120 nickel-based alloy, as well as the amount of cold rolling deformation and heat treatment temperature, without adversely affecting the performance of N08120 nickel-based alloy seamless tubes.

[0028] 2. The method for preparing N08120 nickel-based alloy seamless tubes provided by this invention achieves the requirement of coarse equiaxed grain structure in nickel-based alloy seamless tubes. The prepared seamless tubes have good high-temperature stability, corrosion resistance and mechanical properties, high dimensional accuracy and good surface quality. They can be used in the field of structural materials such as furnace tubes, heating tubes and heat storage devices of various specifications, improve the stability and corrosion resistance of structural materials, and have important significance for actual production. Attached Figure Description

[0029] Figure 1 This is a photograph of the microstructure of a seamless tube with a diameter of Φ114.3*10.7mm in Embodiment 1 of the present invention.

[0030] Figure 2 This is a photograph of the microstructure of the Φ45*6.75mm seamless tube in Embodiment 2 of the present invention;

[0031] Figure 3 This is a photograph of the microstructure of a seamless tube with a diameter of 88.9*6.45mm in Embodiment 3 of the present invention.

[0032] Figure 4 This is a photograph of the microstructure of a seamless tube with a diameter of Φ114.3*10.7mm in Comparative Example 1 of the present invention;

[0033] Figure 5 This is a photograph of the microstructure of the seamless tube with a diameter of Φ114.3*10.7mm in Comparative Example 2 of the present invention;

[0034] Figure 6 This is a photograph of the microstructure of a 114.3*10.7mm seamless tube in Comparative Example 3 of the present invention;

[0035] Figure 7 This is a photograph of the microstructure of the seamless tube with a diameter of Φ114.3*10.7mm in Comparative Example 4 of the present invention;

[0036] Figure 8This is a photograph of the microstructure of a seamless tube with a diameter of 114.3*10.7mm in Comparative Example 5 of this invention. Detailed Implementation

[0037] The technical solution of the present invention will be further described below with reference to specific embodiments. However, the specific details of the embodiments are only for illustrating the present invention and do not represent all technical methods under the concept of the present invention. Therefore, they should not be construed as limiting the overall technical solution of the present invention.

[0038] Example 1

[0039] Preparation of N08120 nickel-based alloy seamless tube with specifications of Φ114.3*10.7mm.

[0040] The N08120 nickel-based alloy round steel with a diameter of 204 mm was obtained by ladle refining and electroslag remelting in an electric arc furnace, followed by hot forging with a forging ratio of 4.5. The chemical composition and weight percentage (%) of the N08120 nickel-based alloy round steel are shown in Table 1.

[0041] Table 1. Chemical composition and weight percentage (%) of N08120 nickel-based alloy round steel.

[0042]

[0043] Round steel bars with a diameter of 204mm and a length of 5m are cut into short pieces with a length of 45cm. The short pieces are drilled, chamfered, and cleaned. Then, they are preheated at 900℃ for 1.2 hours in an annular heating furnace, and then heated to 1190℃ in a primary induction heating furnace. After reaming, they are heated to 1200℃ in a secondary induction heating furnace. Finally, they are hot extruded on a 4200t hot extrusion press at an extrusion temperature of 1200℃ and an extrusion ratio of 15 to obtain a Φ141*18.6mm rough tube with good surface quality, uniformity, and no obvious defects that would affect cold rolling. The rough tube is then finished.

[0044] The finished rough tube was cold rolled on a 110 cold rolling mill from Φ141*18.6mm to Φ114.3*10.7mm with a deformation of 51.31%. After degreasing and heat treatment at 1250℃ for 15 minutes, the tube was pickled, straightened, polished, and finished to obtain a seamless N08120 nickel-based alloy tube with a coarse equiaxed grain structure.

[0045] Metallographic structure, mechanical properties, and corrosion performance were tested on the Φ114.3*10.7mm seamless tube in Example 1. The test results are as follows: Figure 1 As shown in Table 2.

[0046] Table 2 shows the mechanical and corrosion properties of the seamless tubes in Example 1.

[0047]

[0048] Example 2

[0049] Preparation of N08120 nickel-based alloy seamless tube with specifications of Φ45*6.75mm.

[0050] The N08120 nickel-based alloy round steel with a diameter of 204 mm was obtained by ladle refining and electroslag remelting in an electric arc furnace, followed by hot forging with a forging ratio of 4.0. The chemical composition and weight percentage (%) of the N08120 nickel-based alloy round steel are shown in Table 3.

[0051] Table 3 Chemical composition and weight percentage (%) of N08120 nickel-based alloy round steel

[0052]

[0053] Round steel bars with a diameter of 204mm and a length of 4m are cut into short pieces with a length of 45cm. The short pieces are drilled, chamfered, and cleaned. Then, they are preheated at 970℃ for 1.5 hours in an annular heating furnace, and then heated to 1190℃ in a primary induction heating furnace. After reaming, they are heated to 1220℃ in a secondary induction heating furnace. Finally, they are extruded on a 4200t hot extrusion press at a hot extrusion temperature of 1220℃ and a hot extrusion ratio of 18 to obtain a Φ80*8.8mm rough tube with good surface quality, uniformity, and no obvious defects that would affect cold rolling. The rough tube is then finished.

[0054] The finished rough tube was cold rolled on a 60 cold rolling mill from Φ80*8.8mm to Φ45*6.75mm with a deformation of 58.79%. After degreasing and heat treatment at 1210℃ for 14 minutes, the tube was pickled, straightened, polished, and finished to obtain a seamless N08120 nickel-based alloy tube with a coarse equiaxed grain structure.

[0055] The Φ45*6.75mm seamless tube from Example 2 was subjected to metallographic analysis, mechanical property testing, and corrosion performance testing. The test results are as follows: Figure 2 As shown in Table 4.

[0056] Table 4 shows the mechanical and corrosion properties of the seamless tubes in Example 2.

[0057]

[0058] Example 3

[0059] Preparation of N08120 nickel-based alloy seamless tube with specifications of Φ88.9*6.45mm.

[0060] The N08120 nickel-based alloy round steel with a diameter of 204 mm was obtained by ladle refining and electroslag remelting in an electric arc furnace, followed by hot forging with a forging ratio of 5.0. The chemical composition and weight percentage (%) of the N08120 nickel-based alloy round steel are shown in Table 5.

[0061] Table 5 Chemical composition and weight percentage (%) of N08120 nickel-based alloy round steel.

[0062]

[0063]

[0064] Round steel bars with a diameter of 204mm and a length of 2.8m are cut into short pieces with a length of 45cm. The short pieces are drilled, chamfered, and cleaned. Then, they are preheated at 1000℃ for 2 hours in an annular heating furnace, and then heated to 1200℃ in a primary induction heating furnace. After reaming, they are heated to 1250℃ in a secondary induction heating furnace. Finally, they are extruded on a 4200t hot extrusion press at a hot extrusion temperature of 1250℃ and a hot extrusion ratio of 20 to obtain a Φ141*16mm rough tube with good surface quality, uniformity, and no obvious defects that would affect cold rolling. The rough tube is then finished.

[0065] The finished rough tube is cold rolled once on a 110 cold rolling mill, from Φ141*16mm to Φ114.3*10.7mm, with a deformation of 44.57%. It is then degreased, heat-treated at 1200℃ for 25 minutes, pickled, and straightened. It is then cold-rolled twice on a 900 rolling mill, from Φ114.3*10.7mm to Φ88.9*6.45mm, with a deformation of 52.03%. It is then degreased, heat-treated at 1190℃ for 15 minutes, pickled, straightened, and polished. After finishing, a coarse equiaxed grain structure N08120 nickel-based alloy seamless tube is obtained.

[0066] Metallographic structure, mechanical properties, and corrosion performance were tested on the Φ88.9*6.45mm seamless tube in Example 3. The test results are as follows: Figure 3 As shown in Table 6.

[0067] Table 6 shows the mechanical and corrosion properties of the seamless tubes in Example 3.

[0068]

[0069] Comparative Example 1

[0070] The results are basically the same as in Example 1, except that the chemical composition and weight percentage (%) of the N08120 nickel-based alloy round steel in Comparative Example 1 are C = 0.45%, as shown in Table 7.

[0071] Table 7 Chemical composition and weight percentage (%) of N08120 nickel-based alloy round steel

[0072]

[0073] The seamless tube prepared in Comparative Example 1 was subjected to metallographic analysis, mechanical property testing, and corrosion performance testing. The test results are as follows: Figure 4 As shown in Table 8.

[0074] Table 8 shows the mechanical and corrosion properties of seamless tubes in Comparative Example 1.

[0075]

[0076] Comparative Example 2

[0077] The results are basically the same as in Example 1, except that the deformation of the cold rolling process in Comparative Example 2 is 49.45% (Φ141*17.8mm rolled to Φ114.3*10.7mm).

[0078] The seamless tube prepared in Comparative Example 2 was subjected to metallographic analysis, mechanical property testing, and corrosion performance testing. The test results are as follows: Figure 5 As shown in Table 9.

[0079] Table 9 shows the mechanical and corrosion properties of seamless tubes in Comparative Example 2.

[0080]

[0081] Comparative Example 3

[0082] It is basically the same as Example 1, except that the heat treatment temperature after cold rolling in Comparative Example 3 is 1180°C.

[0083] Metallographic structure, mechanical properties, and corrosion properties of the seamless tube prepared in Comparative Example 3 were tested. The test results are as follows: Figure 6 As shown in Table 10.

[0084] Table 10 shows the mechanical and corrosion properties of seamless tubes in Comparative Example 3.

[0085]

[0086] Comparative Example 4

[0087] It is basically the same as Example 1, except that the forging ratio of hot forging in Comparative Example 4 is 3.5.

[0088] Metallographic structure, mechanical properties, and corrosion properties of the seamless tube prepared in Comparative Example 4 were tested. The test results are as follows: Figure 7 As shown in Table 11.

[0089] Table 11 shows the mechanical and corrosion properties of seamless tubes in Comparative Example 4.

[0090]

[0091] Comparative Example 5

[0092] It is basically the same as Example 1, except that the extrusion ratio of the hot extrusion treatment in Comparative Example 5 is 13.

[0093] Metallographic structure, mechanical properties, and corrosion properties of the seamless tube prepared in Comparative Example 5 were tested. The test results are as follows: Figure 8 As shown in Table 12.

[0094] Table 12 shows the mechanical and corrosion properties of seamless tubes in Comparative Example 5.

[0095]

[0096] Comparison of metallographic images of the seamless tubes reveals that the N08120 nickel-based alloy seamless tubes prepared in the examples all exhibit a clear and uniform coarse equiaxed crystal structure, while the seamless tubes in the comparative example show a clear mixed crystal structure.

[0097] A comparison of the mechanical and corrosion performance test results of the seamless tubes in Examples 1-3 and Comparative Examples 1-5 revealed that the seamless tubes prepared by the present invention, through reasonable control of the element content, cold rolling deformation, and heat treatment temperature in the nickel-based alloy, simultaneously possess excellent high-temperature stability, corrosion resistance, and mechanical properties. Specifically, in Comparative Examples 1 and 2, the reduction in carbon content and deformation amount, respectively, led to a decrease in the mechanical properties, high-temperature performance, and corrosion resistance of the seamless tubes. Furthermore, a mixed-grain structure appeared in Comparative Example 2, failing to meet the high-temperature service conditions of the material. In Comparative Example 3, although the decrease in heat treatment temperature did not significantly change the room-temperature mechanical properties, its high-temperature performance and corrosion resistance both showed a significant decline.

Claims

1. A method for preparing a seamless N08120 nickel-based alloy tube with a coarse equiaxed grain structure, characterized in that, Includes the following steps: S1. Refining and electroslag remelting are carried out in an electric arc furnace, followed by hot forging to obtain N08120 nickel-based alloy round steel. S2. Cut the round steel in step S1 into short pieces, then drill holes, chamfer, and clean the short pieces. Then heat them in a primary induction heating furnace, expand the holes, heat them in a secondary induction heating furnace, and finally perform hot extrusion to obtain a rough tube. S3. The rough tube from step S2 is cold rolled into a tube of the required specifications. S4. The tube from step S3 is sequentially subjected to degreasing, heat treatment, pickling, straightening, and polishing. After finishing, a coarse equiaxed crystal structure N08120 nickel-based alloy seamless tube is obtained. In step S1, the composition and weight percentage of the N08120 nickel-based alloy round steel are as follows: 0.05%≤C≤0.10%; Si≤1.0%; Mn≤1.5%; S≤0.03%; 36.0%≤Ni≤39.0%; Cu≤0.50%; Mo≤2.50%; 25.0%≤Cr≤27.0%; Al≤0.40%; Ti≤0.20%; P≤0.04%; B≤0.010%; Co≤3.0%; 0.45%≤Nb≤0.9%; W≤2.5%; 0.15%≤N≤0.30%; Fe = balance; In step S1, the forging ratio of the hot forging process is not less than 4.0; During the cold rolling process in step S3, the deformation amount in a single step shall be ≥50% at least. In step S4, the temperature of the heat treatment is 1190~1250℃.

2. The method for preparing a seamless N08120 nickel-based alloy tube with a coarse equiaxed grain structure according to claim 1, characterized in that, In step S2, before heating in the induction heating furnace, the cleaned short material is preheated to 900~1000℃ for 1~2 hours.

3. The method for preparing a seamless N08120 nickel-based alloy tube with a coarse equiaxed grain structure according to claim 1, characterized in that, In step S2, the extrusion temperature of the hot extrusion treatment is 1180~1250℃, and the extrusion ratio is 15~20.

4. The method for preparing a seamless N08120 nickel-based alloy tube with a coarse equiaxed grain structure according to claim 1, characterized in that, The rough pipes obtained in step S2 still need to undergo finishing processing.

5. The method for preparing a seamless N08120 nickel-based alloy tube with a coarse equiaxed grain structure according to claim 1, characterized in that, In step S3, if the cold rolling process involves multiple passes, the pipe needs to be degreased, heat-treated, pickled, and straightened sequentially after each pass.

6. A seamless tube of N08120 nickel-based alloy with a coarse equiaxed grain structure, characterized in that, It is prepared by any one of claims 1 to 5.

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