A high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high-temperature concentrated sulfuric acid and nitric acid and a preparation method thereof

Abstract

The present invention provides a high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high-temperature concentrated sulfuric acid and concentrated nitric acid, and a preparation method thereof, which solves the technical problem of the lack of UNS S32615 high-silicon stainless steel cold-rolled pipe preparation process in the prior art. The method of the present invention comprises the following steps: peeling, cutting, punching holes and end surface processing of the S32615 rod blank to obtain a stainless steel extruded tube blank; extruding the rough tube through a hot extrusion unit; performing solid solution heat treatment on the intermediate tube; pickling to remove the oxide scale; grinding and polishing the inner and outer surfaces; performing multiple cold rolling deformations using a two-roll cold rolling tube mill; S7, performing gas-protected bright solid solution heat treatment on the finished tube. The preparation method of the present invention can produce UNS S32615 cold-rolled stainless steel pipes with high dimensional accuracy, high surface quality and excellent mechanical properties, which meet the requirements of resistance to sulfuric acid and nitric acid corrosion, and the pipes are tested by mechanical properties, uniform corrosion tests and non-destructive flaw detection, all of which meet the requirements of relevant standards and are suitable for applications in high temperature and high corrosion environments.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel pipe preparation, and in particular to a high-temperature resistant concentrated sulfuric acid and nitric acid resistant, difficult-to-deform high-silicon austenitic stainless steel pipe and a preparation method thereof. Background Art

[0002] High silicon austenitic stainless steel has excellent corrosion resistance, especially in extreme corrosive environments such as high temperature concentrated sulfuric acid and concentrated nitric acid. UNS S32615 is a typical high silicon austenitic stainless steel, the main chemical components include carbon (C ≤ 0.07), nickel (Ni: 19-22), chromium (Cr: 16.5-19.5), silicon (Si: 4.8-6.0), molybdenum (Mo: 0.3-1.5), copper (Cu: 1.5-2.5), manganese (Mn: ≤ 2.0), the reasonable ratio of these elements gives the steel excellent resistance to high temperature concentrated sulfuric acid and concentrated nitric acid corrosion, and has good mechanical properties, and is widely used in the field of chemical equipment.

[0003] However, although the addition of silicon enhances corrosion resistance, it also significantly increases the strength and hardness of the steel, which deteriorates its processing performance. High-silicon austenitic stainless steel is difficult to deform and easy to crack during deformation processes such as cold rolling and cold drawing, which poses great technical challenges to the preparation of pipes. At the same time, high silicon content is also prone to sensitized intergranular corrosion, surface quality defects and reduced welding performance, further limiting its promotion in engineering applications.

[0004] At present, there is still a lack of mature process research in China for the preparation technology of high-silicon austenitic stainless steel pipes, especially UNS S32615 cold-rolled pipes, and there are few related research reports internationally. Most of the existing technical methods are limited to hot extrusion or simple cold processing processes, which are difficult to meet the requirements of high dimensional accuracy and high surface quality. Especially for the use of pipes in high-temperature acidic media, the performance of steel pipes prepared by traditional methods in terms of mechanical properties, uniform corrosion rate and non-destructive testing is often difficult to meet strict industrial standards.

[0005] In addition, in the existing preparation methods, the process links such as pickling, grinding and polishing, and solution heat treatment of the pipe lack optimized design, which leads to defects such as scale, cracks, and pitting on the surface of the pipe, affecting the subsequent cold processing quality and the performance stability of the finished pipe. Therefore, developing an efficient preparation method suitable for high-silicon austenitic stainless steel pipes, especially UNS S32615 alloy cold-rolled pipes, has become an important research direction to solve the current technical bottleneck. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a high-silicon austenitic stainless steel pipe that is difficult to deform and is resistant to high temperature concentrated sulfuric acid and concentrated nitric acid, which solves the problems of difficult processing, poor pipe dimensional accuracy, low surface quality and insufficient comprehensive performance existing in the conventional preparation methods in the prior art.

[0007] In order to overcome the above defects of the prior art, the present invention provides a method for preparing a high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high temperature concentrated sulfuric acid and concentrated nitric acid, which is characterized by comprising the following steps:

[0008] S1: peeling, cutting, punching and end surface processing of S32615 rod blank to obtain stainless steel extruded tube blank;

[0009] S2: hot extruding the tube blank on a hot extruder to form a rough tube;

[0010] S3: performing a solution heat treatment on the rough pipe, wherein the solution temperature is 1020° C. to 1070° C.;

[0011] S4: pickling the stainless steel tube after solid solution, wherein the pickling adopts HNO3+HF mixed acid solution;

[0012] S5: performing surface treatment on the stainless steel pipe after pickling in step S4 to obtain a finished pipe, and further performing polishing on the finished pipe;

[0013] S6: cold rolling the finished tube obtained in step S5 at least three times using a two-roller cold rolling mill;

[0014] S7: The cold-rolled pipe is subjected to gas protection bright solution heat treatment to obtain a high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high-temperature concentrated sulfuric acid and nitric acid.

[0015] Compared with the prior art, the preparation method of the high-silicon austenitic stainless steel pipe resistant to high temperature concentrated sulfuric acid and concentrated nitric acid has the following advantages: the preparation method of the present invention successfully overcomes the defects of high-silicon stainless steel being difficult to deform and easy to crack during cold working by designing a hot extrusion (S2) + multi-pass cold rolling deformation (S6) process; the combination of multiple cold rolling and solution treatment (S3 and S7) further improves the plasticity and processability of the pipe; and through pickling (S4) and surface grinding and polishing (S5), it is ensured that there are no defects such as oxide scale, residual acid, cracks, and scars on the inner and outer surfaces of the pipe, meeting the requirements for high surface quality of the pipe. And through multiple cold rolling and solution heat treatment processes (S7), the finished pipe has excellent comprehensive mechanical properties, including higher tensile strength, yield strength and elongation after fracture, and the corrosion resistance to high-temperature concentrated sulfuric acid and concentrated nitric acid is greatly improved; the preparation method of the present invention optimizes the hot extrusion, cold rolling deformation and heat treatment processes to achieve a comprehensive improvement in the corrosion resistance, mechanical properties, surface quality and dimensional accuracy of high-silicon austenitic stainless steel pipes, solves the problems of difficult processing and unstable quality of high-silicon stainless steel pipes in the prior art, and successfully prepares seamless precision pipes that meet the requirements of high-temperature concentrated sulfuric acid and concentrated nitric acid working conditions.

[0016] In a possible implementation, in the step S1, the S32615 rod blank is obtained by subjecting the raw materials to electric furnace, refining outside the furnace, or by subjecting the raw materials to medium frequency induction and electroslag remelting.

[0017] Compared with the prior art, the above-mentioned technical scheme is adopted, through the electric furnace + out-of-furnace refining process or the medium frequency induction + electroslag remelting process, which can effectively remove harmful impurities (such as S, P, etc.) in the raw materials and further improve the purity of stainless steel; the electroslag remelting process can achieve efficient degassing and deoxidation, eliminate inclusions, and at the same time improve the uniformity of alloy composition, ensure the metallurgical quality of the material, further realize the precise control of chemical composition and the effective elimination of metallurgical defects, and finally improve the processing performance and corrosion resistance of stainless steel pipes, ensuring that the present invention can smoothly prepare high-quality and high-dimensional precision finished pipes.

[0018] In a possible embodiment, in step S4, the pickling step includes: pickling the stainless steel pipe after solution treatment with HNO3+HF mixed acid solution at a temperature below 65°C, and observing it once during the pickling process, and flushing it with high-pressure water and assisted by manual scrubbing to ensure that there is no oxide scale, residual acid, dirt, or oil on the inner and outer surfaces of the rough pipe after pickling, and the pickling time is 10-30 minutes.

[0019] Compared with the prior art, the above-mentioned technical scheme is adopted to design a mixed acid solution of HNO3 (nitric acid) and HF (hydrofluoric acid) with strong oxidizing and dissolving ability, which can effectively remove the oxide scale and passivation film on the surface of stainless steel. Nitric acid is mainly used to dissolve the oxide scale, while hydrofluoric acid can quickly remove the insoluble silicate oxides, especially the oxide scale attached to the surface of high-silicon stainless steel. Further, by controlling the pickling temperature below 65°C, it can effectively avoid high temperature accelerating corrosion reaction and ensure the integrity of the pipe surface; the pickling time is controlled at 10-30min to avoid damage to the stainless steel matrix caused by excessive pickling; and combined with the cylinder observation, high-pressure water washing and manual scrubbing steps, the problems of uneven pickling, residual oxide scale and matrix damage in the prior art are solved, and the high surface quality of high-silicon austenitic stainless steel pipes and good pretreatment effect before cold rolling are achieved, providing reliable technical guarantee for subsequent processes.

[0020] In a possible implementation, in step S5, the surface treatment includes: performing white corundum grinding wheel + flap wheel grinding and polishing, flap wheel grinding and polishing steps on the stainless steel pipe in sequence, and after the surface treatment, the surface of the stainless steel pipe has no cracks, folds, scars, pitting and pitting defects, thereby meeting the subsequent cold processing requirements.

[0021] Compared with the existing technology, the above technical scheme is adopted, through the step-by-step grinding and polishing process of white corundum grinding wheel + thousand-blade wheel, various defects on the surface of stainless steel pipes are effectively removed, the smoothness and uniformity of the pipe surface are ensured, and the problem of surface defects affecting the subsequent cold rolling process in the existing technology is avoided. Finally, the preparation of high-quality, high-precision and high-stability high-temperature resistant concentrated sulfuric acid and concentrated nitric acid stainless steel pipes is achieved.

[0022] In a possible implementation, in step S5, the polishing process includes: polishing the surface of the finished tube by a belt polisher, wherein the belt polisher uses a fine sand belt with a mesh of ≥800 for polishing, and the surface roughness of the finished tube after polishing is ≤Ra0.6μm.

[0023] Compared with the prior art, the above technical solution is adopted to effectively remove tiny flaws and rough textures on the surface of stainless steel pipes by using a belt polisher combined with a fine sand belt of ≥800 mesh for polishing, and achieve a surface roughness standard of Ra≤0.6μm, thereby significantly improving the surface quality and corrosion resistance of the pipes, solving the technical problems of high and uneven surface roughness in the prior art, and meeting the demand for high surface precision pipes in special environments such as high-temperature concentrated sulfuric acid and concentrated nitric acid.

[0024] In a possible implementation, in step S6, the conditions for cold rolling include: cold rolling the finished tube at least three times through a two-roll cold rolling mill through different types of cold rolling mills, and the rolling parameters of the cold rolling mill include: LG60 rolling mill, speed ≤60 times / min, feed amount ≤3mm / time; LG50 rolling mill, speed ≤70 times / min, feed amount ≤2mm / time; LG30 rolling mill, speed ≤70 times / min, feed amount ≤1.5mm / time.

[0025] Compared with the prior art, the above technical scheme is adopted to perform at least 3 cold rolling deformations through a two-roll cold rolling tube mill, gradually reduce the wall thickness and diameter of the tube, evenly distribute the cold working deformation, effectively improve the dimensional accuracy and surface quality, and adopt different types of cold rolling mills such as LG60, LG50 and LG30 according to different cold rolling stages, and set specific vehicle speed and feed amount parameters to ensure that the deformation amount of each pass is controlled within a reasonable range to prevent the tube from cracking or uneven wall thickness. By gradually decreasing the feed amount and precise vehicle speed control, the risk of stress concentration during the cold rolling process is reduced, and high-precision deformation and wall thickness control are achieved, thereby effectively improving the dimensional accuracy, surface quality and wall thickness uniformity of the finished tube, and reducing the risk of defects during the deformation process; and the multiple cold rolling of the above-mentioned step S6 of the present invention further cooperates with the operations of steps S5 and S7: step S6, on the basis of step S5, combines the pretreatment of surface defects with fine cold rolling, which can effectively reduce The risk of defect expansion is reduced, and the comprehensive quality and cold rolling processing accuracy of the pipe are improved; and the multiple cold rolling deformation in step S6 can improve the internal organization of the pipe and increase the dimensional accuracy of the pipe, but it will also introduce higher residual stress. Combined with the gas protection bright solution heat treatment process in step S7, by heating to 990℃~1040℃, the residual stress generated during the cold rolling process is effectively eliminated, the plasticity and toughness of the pipe are restored, and the grain uniformity is improved, and the organizational performance is optimized. The synergistic effect of the two, the high strength introduced by cold rolling and the organizational recovery of the solution treatment are combined, which not only ensures the high dimensional accuracy of the pipe, but also achieves excellent mechanical properties and corrosion resistance; through the synergistic effect of the above steps S5-S7, the comprehensive optimization of the surface quality, dimensional accuracy, mechanical properties and corrosion resistance of the pipe is achieved, which meets the application requirements of high-precision and high-performance pipes in high-temperature concentrated sulfuric acid and concentrated nitric acid environments, and solves the technical problems of many surface defects, poor dimensional accuracy, insufficient mechanical properties and corrosion resistance in the prior art.

[0026] In a possible implementation, in step S7, the temperature of the solution heat treatment is 990°C to 1040°C.

[0027] Compared with the prior art, the above technical scheme is adopted, and the solution heat treatment is an essential key step in the production process of high-silicon austenitic stainless steel pipes. By heating to a high temperature range of 990℃~1040℃, the carbides, inclusions and structural inhomogeneities inside the pipe can be effectively eliminated, and at the same time, the alloy elements (such as Si, Cr, Ni, etc.) are re-dissolved uniformly in the austenite matrix; in addition, the solution heat treatment in the present invention can effectively eliminate the residual stress introduced during the cold rolling process, improve the plasticity and toughness of the pipe, and restore its mechanical properties. The temperature range of 990℃~1040℃ is an optimized value, which can not only ensure the full solution of the organization, but also avoid the grain coarsening caused by excessive temperature, thereby obtaining a fine and uniform grain structure.

[0028] Another technical problem to be solved by the present invention is to provide a high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high temperature concentrated sulfuric acid and concentrated nitric acid, so as to solve the problems of poor corrosion resistance, insufficient mechanical properties, and difficulty in meeting the requirements for dimensional accuracy and surface quality of finished pipes existing in conventional stainless steel pipes in the prior art.

[0029] The present invention also provides a high-silicon austenitic stainless steel pipe that is difficult to deform and is resistant to high-temperature concentrated sulfuric acid and nitric acid. The stainless steel pipe is prepared by the above-mentioned preparation method.

[0030] Compared with the prior art, the high-silicon austenitic stainless steel pipe resistant to high temperature concentrated sulfuric acid and concentrated nitric acid has the following advantages: through the design of high-purity S32615 alloy components and the optimized preparation process, especially the synergistic effect of solid solution heat treatment, cold rolling process and surface treatment, the internal structure of the pipe is more uniform, the grain is refined, and the surface quality is excellent. Through the combination of surface polishing and pickling process, the surface oxide scale, residual acid and defects are removed, ensuring the stability of the pipe in the environment of high concentration sulfuric acid and nitric acid, and the cold rolling parameter optimization and multi-pass deformation treatment, the pipe obtains high-precision size control and excellent mechanical properties; and the stainless steel of the present invention The pipe's ability to resist sulfuric acid and nitric acid corrosion is far superior to existing conventional stainless steel materials, and its uniform austenite matrix structure reduces local corrosion sensitivity; the residual stress of the pipe in the present invention is eliminated through solid solution treatment, which effectively improves the service life and stability of the material, and solves the problem of easy cracking and failure of traditional pipes. The stainless steel pipe in the present invention solves the corrosion performance, mechanical properties and surface quality problems of conventional pipes in the prior art, and finally produces a high-silicon austenitic stainless steel pipe with high corrosion resistance, excellent mechanical properties, high precision and high surface quality that is difficult to deform and resistant to high temperature concentrated sulfuric acid and nitric acid, meeting the needs of high-end industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a uniform corrosion test diagram of Example 1 / 2 in 98% sulfuric acid solution at 90°C;

[0032] Figure 2 This is a uniform corrosion test diagram of Example 1 / 2 in 93% sulfuric acid solution at 90°C. DETAILED DESCRIPTION

[0033] First, those skilled in the art should understand that these implementations are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0034] The present invention provides a method for preparing a high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high-temperature concentrated sulfuric acid and nitric acid, comprising the following steps:

[0035] S1: peeling, cutting, punching and end surface processing of S32615 rod blank to obtain stainless steel extruded tube blank;

[0036] S2: hot extruding the tube blank on a hot extruder to form a rough tube;

[0037] S3: performing a solution heat treatment on the rough pipe, wherein the solution temperature is 1020° C. to 1070° C.;

[0038] S4: pickling the stainless steel tube after solid solution, wherein the pickling adopts HNO3+HF mixed acid solution;

[0039] S5: performing surface treatment on the stainless steel pipe after pickling in step S4 to obtain a finished pipe, and further performing polishing on the finished pipe;

[0040] S6: cold rolling the finished tube obtained in step S5 at least three times using a two-roller cold rolling mill;

[0041] S7: The cold-rolled pipe is subjected to gas protection bright solution heat treatment to obtain a high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high-temperature concentrated sulfuric acid and nitric acid.

[0042] As a preferred solution, in the step S1, the S32615 rod blank is obtained by subjecting the raw materials to electric furnace, refining outside the furnace, or medium frequency induction and electroslag remelting.

[0043] As a preferred solution, in step S4, the pickling step includes: pickling the stainless steel pipe after solution treatment with HNO3+HF mixed acid solution at a temperature below 65°C, and observing it once during the pickling process, and flushing it with high-pressure water and assisted by manual scrubbing to ensure that there is no oxide scale, residual acid, dirt, or oil on the inner and outer surfaces of the rough pipe after pickling, and the pickling time is 10-30 minutes.

[0044] As a preferred solution, in step S5, the surface treatment includes: performing white corundum grinding wheel + flap wheel grinding and polishing, flap wheel grinding and polishing steps on the stainless steel pipe in sequence, and after the surface treatment, the surface of the stainless steel pipe is free of cracks, folds, scars, pitting and pitting defects, thereby meeting the subsequent cold processing requirements.

[0045] As a preferred solution, in step S5, the polishing process includes: polishing the surface of the finished tube by a belt polisher, wherein the belt polisher uses a fine sand belt with a mesh of ≥800 for polishing, and the surface roughness of the finished tube after polishing is ≤Ra0.6μm.

[0046] As a preferred solution, in step S6, the conditions for cold rolling include: cold rolling the finished pipe at least three times through a two-roll cold rolling mill through different types of cold rolling mills, and the rolling parameters of the cold rolling mill include: LG60 rolling mill, speed ≤60 times / min, feed amount ≤3mm / time; LG50 rolling mill, speed ≤70 times / min, feed amount ≤2mm / time; LG30 rolling mill, speed ≤70 times / min, feed amount ≤1.5mm / time.

[0047] As a preferred solution, in step S7, the temperature of the solution heat treatment is 990°C to 1040°C.

[0048] The present invention also provides a high-silicon austenitic stainless steel pipe that is difficult to deform and is resistant to high-temperature concentrated sulfuric acid and nitric acid. The stainless steel pipe is prepared by the above-mentioned preparation method.

[0049] The following provides an embodiment combined with specific data in combination with the above technical solution to further explain the above-mentioned scope of the invention:

[0050] Embodiment 1:

[0051] The present invention provides a high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high-temperature concentrated sulfuric acid and nitric acid, and a preparation method thereof. The high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high-temperature concentrated sulfuric acid and nitric acid is prepared by the preparation method, and the preparation method comprises the following steps:

[0052] S1: It is produced by forging or rolling using electric furnace + external refining or medium frequency induction + electroslag remelting process. The S32615 rod billet is subjected to peeling, cutting, punching and end surface processing to obtain a stainless steel extruded tube billet.

[0053] S2: The tube blank is hot extruded by a 35MN hot extrusion unit to form a rough tube with a specification of Φ89×9mm.

[0054] S3: performing solution heat treatment on the rough pipe, with the solution temperature controlled at 1050°C, and using a natural gas heated roller hearth continuous furnace or a hydrogen protected bright furnace for solution treatment.

[0055] S4: The stainless steel pipe after solid solution is pickled with HNO3+HF mixed acid solution at a temperature below 65°C for 20 minutes. During the pickling period, the pipe is taken out of the tank for observation once, and is rinsed with high-pressure water and manually scrubbed to ensure that there is no oxide scale, residual acid, dirt, or oil on the inner and outer surfaces of the pipe after pickling.

[0056] S5: Surface treatment of the pickled rough pipe, including:

[0057] The rough pipe is ground and polished with white corundum grinding wheel + thousand-blade wheel;

[0058] The inner and outer surfaces of the pipe are further ground and polished using a flap wheel to ensure that the surface is free of cracks, folds, scars, pitting and other defects to meet the requirements of subsequent cold rolling processing.

[0059] S6: Use LG60, LG50 and LG30 two-roller cold rolling mills to perform four-pass cold rolling deformation. The specific process parameters are as follows:

[0060] First pass: LG60 rolling mill, specification 65*4.5mm, dimensional tolerance ±0.20, speed ≤60 times / min, feed amount ≤3mm / time, heat treatment temperature 1040~1060℃, time 25~30min;

[0061] Second pass: LG60 rolling mill, specification 48.3*3mm, dimensional tolerance ±0.10, speed ≤60 times / min, feed amount ≤3mm / time, heat treatment temperature 1040~1060℃, time 20~25min;

[0062] The third pass: LG50 rolling mill, specification 32*2mm, dimensional tolerance ±0.10, speed ≤70 times / min, feed amount ≤2mm / time, heat treatment temperature 1020~1040℃, time 10~12min;

[0063] Fourth pass: LG30 rolling mill, specification 19.05*1.3mm, dimensional tolerance D: +0.06 / +0.08mm, S: ±0.05mm, speed ≤70 times / min, feed amount ≤1.5mm / time, heat treatment temperature 1000~1020℃, time 7~10min.

[0064] See Table 2 below for details:

[0065] Table 2 Cold working and heat treatment process of S32615 pipe

[0066] S7: The finished tube after cold rolling is subjected to gas protection bright solution heat treatment, and the heat treatment temperature is controlled at 1010℃. UNS S32615 high silicon stainless steel precision steel pipe.

[0067] Embodiment 2:

[0068] The present invention provides a high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high-temperature concentrated sulfuric acid and nitric acid, and a preparation method thereof. The high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high-temperature concentrated sulfuric acid and nitric acid is prepared by the preparation method, and the preparation method comprises the following steps:

[0069] S1: It is produced by forging or rolling using electric furnace + external refining or medium frequency induction + electroslag remelting process. The S32615 rod billet is subjected to peeling, cutting, punching and end surface processing to obtain a stainless steel extruded tube billet.

[0070] S2: The tube blank is hot extruded by a 35MN hot extrusion unit to form a rough tube with a specification of Φ65×5.5 mm.

[0071] S3: performing solution heat treatment on the rough pipe, with the solution temperature controlled at 1040°C, and using a natural gas heated roller hearth continuous furnace or a hydrogen protected bright furnace for solution treatment.

[0072] S4: The stainless steel pipe after solid solution is pickled with HNO3+HF mixed acid solution at a temperature below 65°C for 10 minutes. During the pickling period, the pipe is taken out of the tank for observation once, and is rinsed with high-pressure water and manually scrubbed to ensure that there is no oxide scale, residual acid, dirt, or oil on the inner and outer surfaces of the pipe after pickling.

[0073] S5: Surface treatment of the pickled rough pipe, including:

[0074] The rough pipe is ground and polished with white corundum grinding wheel + thousand-blade wheel;

[0075] The inner and outer surfaces of the pipe are further ground and polished using a flap wheel to ensure that the surface is free of cracks, folds, scars, pitting and other defects to meet the requirements of subsequent cold rolling processing.

[0076] S6: Use LG60, LG50 and LG30 two-roller cold rolling mills to perform three-pass cold rolling deformation. The specific process parameters are as follows:

[0077] First pass: LG60 rolling mill, specification 48.3*3mm, speed ≤60 times / min, feed amount ≤3mm / time, heat treatment temperature 1050~1070℃, time 20~25min;

[0078] Second pass: LG50 rolling mill, specification 32*2mm, speed ≤70 times / min, feed amount ≤2mm / time, heat treatment temperature 1020~1040℃, time 10~12min;

[0079] The third pass: LG30 rolling mill, specification 19.05*1.3mm, speed ≤70 times / min, feed amount ≤1.5mm / time, dimensional tolerance D: +0.06 / +0.08mm, S: ±0.05mm, heat treatment temperature 1000~1020℃, time 7~10min.

[0080] See Table 3 below for details:

[0081] Table 3 Cold working and heat treatment process of S32615 pipe

[0082]

[0083]

[0084] S7: The finished cold-rolled tube is subjected to gas protection bright solution heat treatment, and the heat treatment temperature is controlled at 1000°C. UNS S32615 high silicon stainless steel precision steel pipe.

[0085] Embodiment 3:

[0086] The present invention provides a high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high-temperature concentrated sulfuric acid and nitric acid, and a preparation method thereof. The high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high-temperature concentrated sulfuric acid and nitric acid is prepared by the preparation method, and the preparation method comprises the following steps:

[0087] S1: It is produced by forging or rolling using electric furnace + external refining or medium frequency induction + electroslag remelting process. The S32615 rod billet is subjected to peeling, cutting, punching and end surface processing to obtain a stainless steel extruded tube billet.

[0088] S2: The tube blank is hot extruded by a 35MN hot extrusion unit to form a rough tube with a specification of Φ89×9mm.

[0089] S3: performing solution heat treatment on the rough pipe, with the solution temperature controlled at 1060°C, and using a natural gas heated roller bottom continuous furnace or a hydrogen protected bright furnace for solution treatment.

[0090] S4: The stainless steel pipe after solid solution is pickled with HNO3+HF mixed acid solution at below 65°C for 30 minutes. During this period, it is observed once and rinsed with high-pressure water and manually scrubbed to ensure that there is no oxide scale, residual acid, dirt or oil on the inner and outer surfaces of the pipe after pickling.

[0091] S5: Surface treatment of the pickled rough pipe, including:

[0092] The rough pipe is ground and polished with white corundum grinding wheel + thousand-blade wheel;

[0093] The inner and outer surfaces of the pipe are further ground and polished using a flap wheel to ensure that the surface is free of cracks, folds, scars, pitting and other defects to meet the requirements of subsequent cold rolling processing.

[0094] S6: Using LG60, LG50 and LG30 two-roller cold rolling mills, three passes of cold rolling deformation are performed. The specific process parameters are the same as those in Example 2.

[0095] S7: The finished cold-rolled tube is subjected to gas-protected bright solution heat treatment, and the heat treatment temperature is controlled at 1020°C to finally obtain UNS S32615 high-silicon stainless steel precision steel tube.

[0096] Performance testing: The cold-rolled tubes prepared in the above-mentioned embodiments 1 / 2 of the present invention were tested for relevant performances, as follows:

[0097] 1. Detection of mechanical properties and high-magnification grain size of the cold-rolled tubes prepared in Example 1 and Example 2

[0098] (1) Testing standards

[0099] The mechanical properties, flattening test and grain size meet the requirements of ASME SA-312 / SA-312M "Seamless and Welded Austenitic Stainless Steel Pipes", as shown in Table 4.

[0100] Table 4 Pipe performance table

[0101]

[0102] (2) The pipe is subjected to a uniform corrosion test in a 98% sulfuric acid solution at 90°C according to JB / T 7901-2023 "Metallic Materials Laboratory Uniform Corrosion Full Immersion Test Method", and the average corrosion rate is <0.018mm / year.

[0103] The pipe was subjected to a uniform corrosion test in a 93% sulfuric acid solution at 90°C according to JB / T 7901-2023 "Laboratory Uniform Corrosion Full Immersion Test Method for Metal Materials", and the average corrosion rate was <0.049mm / year.

[0104] (3) Test results:

[0105] a) As shown in Table 5 below:

[0106] Table 5 Mechanical properties, flattening, and high-magnification microstructure grain size test results

[0107]

[0108] b) The pipe was subjected to a uniform corrosion test in 98% sulfuric acid solution at 90°C according to JB / T 7901-2023 "Metallic Materials Laboratory Uniform Corrosion Full Immersion Test Method", and the average corrosion rate was measured to be 0.0073mm / year. The pictures of the corrosion samples before and after the test are as follows Figure 1 As shown, Figure 1 It is a uniform corrosion test in 98% sulfuric acid solution at 90°C;

[0109] The pipe was subjected to a uniform corrosion test in a 93% sulfuric acid solution at 90°C according to JB / T 7901-2023 "Metallic Materials Laboratory Uniform Corrosion Full Immersion Test Method". The average corrosion rate was measured to be 0.0032mm / year. Figure 2 As shown in Figure 2, it is a uniform corrosion test in 93% sulfuric acid solution at 90°C.

[0110] Figure 1 , Figure 2 In the test, the appearance of the sample is almost unchanged before and after the test, and no obvious defects such as corrosion, oxidation, and pitting appear on the surface, indicating that the steel pipe prepared by the present invention has an extremely low corrosion rate and excellent corrosion resistance. The high-silicon austenitic stainless steel pipe prepared by Example 1 and Example 2 shows an extremely low corrosion rate in 98% sulfuric acid and 93% sulfuric acid solutions at 90°C. Combined with the mechanical properties and corrosion test results, it is further verified that the comprehensive performance of the stainless steel pipe prepared by the preparation method of the present invention fully meets the technical requirements of the actual use environment, and solves the technical problems of high-silicon stainless steel being difficult to deform and corrosion resistant.

[0111] 2. Nondestructive testing of the cold-rolled tubes prepared in Example 1 and Example 2:

[0112] (1) Testing standards or testing methods

[0113] Nondestructive testing: ASTM E213 standard, standard sample flaw depth meets 12.5% ​​of the wall thickness or 0.1mm (whichever is greater) requirement for ultrasonic testing, or ASTM E426 standard, drilling Through holes are tested by eddy current testing.

[0114] (2) Test results

[0115] Produced according to Example 1 and Example 2 The finished pipes were tested for non-destructive testing according to ASTM E213 and ASTM E426 standards, and the results met the standard requirements.

[0116] The method for preparing the difficult-to-deform high-silicon austenitic stainless steel pipe provided by the present invention can obtain a seamless precision cold-rolled steel pipe with high dimensional accuracy, high surface quality and good comprehensive mechanical properties; the S32615 bar blank prepared by electric furnace + refining outside the furnace or medium frequency induction + electroslag remelting can be used to prepare UNS S32615 high-silicon stainless steel rough pipe that meets the cold processing requirements using the "hot extrusion rough pipe + multi-pass cold rolling deformation" technology; in the above embodiment, the method produced by the present invention The physical properties of UNS S32615 high silicon stainless steel precision steel pipe fully meet the performance index requirements put forward by users; The nondestructive testing of UNS S32615 high silicon stainless steel precision steel pipe fully meets the requirements of the corresponding flaw detection standards, and the steel pipe meets the requirements of high surface quality and high dimensional accuracy.

[0117] In summary, the present invention provides a high-silicon austenitic stainless steel pipe that is resistant to high-temperature concentrated sulfuric acid and nitric acid and is difficult to deform, and a preparation method thereof. The principle is that by reasonably designing the preparation process of the high-silicon austenitic stainless steel pipe, including hot extrusion, solution heat treatment, pickling, grinding and polishing, multi-pass cold rolling deformation, and gas-protected bright solution heat treatment and other steps, the good formability, dimensional accuracy and surface quality of the steel pipe are ensured, and the corrosion resistance is optimized; the present invention achieves the following technical advantages: through hot extrusion + multi-pass cold rolling process, the problem of high silicon austenitic stainless steel being difficult to deform due to high hardness and high strength is successfully solved, and high precision is achieved. The invention relates to pipe processing with high strength and high surface quality; the solution heat treatment and fine surface treatment process are adopted to effectively eliminate the scale and surface defects, and ensure that the surface roughness and smoothness of the pipe meet the technical requirements; the prepared pipes show extremely low corrosion rates in 98% sulfuric acid and 93% sulfuric acid solutions at 90°C, with average corrosion rates of 0.0073mm / year and 0.0032mm / year respectively, showing excellent high-temperature concentrated sulfuric acid and concentrated nitric acid corrosion resistance; the preparation method of the invention adopts efficient heat treatment process and process parameter optimization, and the pipe has high strength, good ductility and stable grain structure, which fully meets the mechanical property requirements of ASME SA-312 and other standards, effectively solves the technical problems of high-silicon austenitic stainless steel pipes in the prior art that are difficult to be cold-rolled, have poor surface quality and unstable corrosion resistance, and provides a feasible and industrialized preparation method, which meets the use requirements in harsh environments such as high-temperature concentrated sulfuric acid and concentrated nitric acid.

[0118] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" etc. means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0119] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for preparing a high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high temperature concentrated sulfuric acid and nitric acid, characterized in that: The following steps are involved: S1: peeling, cutting, punching and end surface processing of S32615 rod blank to obtain stainless steel extruded tube blank; S2: hot extruding the tube blank obtained in step S1 on a hot extruder to form a rough tube; S3: performing a solution heat treatment on the rough pipe obtained in step S2, wherein the solution temperature is 1020° C. to 1070° C.; S4: pickling the stainless steel tube after solid solution in step S3, wherein the pickling adopts HNO3+HF mixed acid solution; S5: performing surface treatment on the stainless steel pipe after pickling in step S4 to obtain a finished pipe, and further performing polishing on the finished pipe; S6: cold rolling the finished tube obtained in step S5 at least three times using a two-roller cold rolling mill; S7: performing gas shielded bright solution heat treatment on the pipe after cold rolling in step S6 to obtain a high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high temperature concentrated sulfuric acid and nitric acid.

2. The method for preparing the high-temperature resistant concentrated sulfuric acid and nitric acid hard-to-deform high-silicon austenitic stainless steel pipe according to claim 1, characterized in that: In the step S1, the S32615 rod blank is obtained by subjecting the raw materials to electric furnace, refining outside the furnace or medium frequency induction and electroslag remelting.

3. The method for preparing the high-temperature resistant concentrated sulfuric acid and nitric acid hard-to-deform high-silicon austenitic stainless steel pipe according to claim 1, characterized in that: In step S4, the pickling step includes: pickling the stainless steel pipe after solution treatment with HNO3+HF mixed acid solution at a temperature below 65°C, and observing once during the pickling process, and flushing with high-pressure water and manual scrubbing to ensure that there is no oxide scale, residual acid, dirt, or oil on the inner and outer surfaces of the rough pipe after pickling, and the pickling time is 10-30 minutes.

4. The method for preparing the high-temperature resistant concentrated sulfuric acid and nitric acid hard-to-deform high-silicon austenitic stainless steel pipe according to claim 1, characterized in that: In step S5, the surface treatment includes: performing white corundum grinding wheel + flap wheel grinding and polishing, flap wheel grinding and polishing steps on the stainless steel pipe in sequence, and after the surface treatment, the surface of the stainless steel pipe has no cracks, folds, scars, pitting and pitting defects, thereby meeting the subsequent cold processing requirements.

5. The method for preparing the high-temperature resistant concentrated sulfuric acid and nitric acid hard-to-deform high-silicon austenitic stainless steel pipe according to claim 1, characterized in that: In the step S5, the polishing process includes: polishing the surface of the finished pipe by a belt polisher, wherein the belt polisher uses a fine sand belt with a mesh of ≥800 for polishing, and the surface roughness of the finished pipe after polishing is ≤Ra0.6μm.

6. The method for preparing the high-temperature resistant concentrated sulfuric acid and nitric acid hard-to-deform high-silicon austenitic stainless steel pipe according to claim 1, characterized in that: In the step S6, the conditions for cold rolling include: the finished tube is cold rolled at least three times by a two-roll cold rolling mill through different types of cold rolling mills, and the rolling parameters of the cold rolling mill include: LG60 rolling mill, speed ≤60 times / min, feed amount ≤3mm / time; LG50 rolling mill, speed ≤70 times / min, feed amount ≤2mm / time; LG30 rolling mill, speed ≤70 times / min, feed amount ≤1.5mm / time.

7. The method for preparing the high-temperature resistant concentrated sulfuric acid and nitric acid hard-to-deform high-silicon austenitic stainless steel pipe according to claim 1, characterized in that: In the step S7, the temperature of the solution heat treatment is 990°C to 1040°C.

8. A high-silicon austenitic stainless steel pipe that is difficult to deform and resistant to high temperature concentrated sulfuric acid and nitric acid, characterized in that: The stainless steel pipe is prepared by the preparation method according to any one of claims 1 to 7.

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