A method for high-precision thin-walled steel pipe based on cold rolling and cold-drawing cooperative deformation

Abstract

The application discloses a kind of based on cold rolling cold-drawing collaborative deformation high-precision thin-walled steel pipe method, it is related to metal material technical field.Process includes: T91 round billet is sequentially carried out heat rolling process, cold rolling process, cold-drawing process, heat treatment process, obtains high-precision T91 thin-walled steel pipe;Again, product size, performance inspection, obtain final product.Through the optimization limitation of process in each process, the wall thickness thinning ability of steel pipe is effectively improved, the wall thickness unevenness control is realized, the surface quality is enhanced, the improvement of comprehensive yield is promoted, so as to meet the lightweight and thin-walled application scene requirement of T91 seamless steel pipe for power plant soot blower.

Description

Technical Field

[0001] This invention relates to the field of metal materials technology, specifically a method for high-precision T91 thin-walled steel pipes based on the coordinated deformation of cold rolling and cold drawing. Background Technology

[0002] Power plant soot blowers are key equipment used to remove ash from the surfaces of boilers, heat exchangers and other equipment. On the one hand, their working environment involves high temperature, high pressure and corrosive media, requiring the seamless steel pipes of their main structure to have certain strength, high temperature creep resistance and corrosion resistance. On the other hand, in order to reduce the load on the installation and support structure and improve the flexibility and responsiveness of equipment operation, the steel pipes need to be lightweight. Among them, seamless steel pipes of ASME SA-213 T91 grade meet the requirements of their service environment. However, the demand for lightweight and thin-walled pipes has placed higher requirements on dimensional accuracy. Taking Φ140×3.5mm steel pipe as an example, the allowable deviation of the outer diameter D (the maximum allowable deviation range between the actual outer diameter and the nominal outer diameter) is ±0.55mm, the maximum value of the outer diameter out-of-roundness Dmax-Dmin (the difference between the maximum and minimum outer diameters on the same cross section of the steel pipe) is 1.10mm; the allowable deviation of the wall thickness S (the maximum allowable deviation range between the actual wall thickness and the nominal wall thickness) is ±0.30mm, and the maximum value of the wall thickness non-uniformity Smax-Smin (the difference between the maximum and minimum wall thicknesses on the same cross section of the steel pipe) is 0.60mm. This far exceeds the standard ASME SA213 (taking Φ140×3.5mm steel pipe as an example, the allowable deviation range of outer diameter D is -1.20~0.40mm, there is no requirement for outer diameter out-of-roundness, the allowable deviation of wall thickness S is 0~1.16mm, and there is no requirement for wall thickness uniformity). Currently, for T91 thin-walled steel pipes, the traditional hot rolling process, due to equipment limitations, can only achieve a minimum wall thickness of 6mm with wide tolerances, which cannot meet the requirements for thinner walls. Currently, only a few companies use the "hot-rolled mother tube + cold forming" process to supply, but it relies on high-precision mother tubes and specialized equipment, which has high technical barriers and high costs, making it difficult to popularize.

[0003] In the existing technology, there are already some invention patents related to solving the problem of achieving large-scale, efficient production of high-precision thin-walled steel pipes; the relevant ones are as follows:

[0004] Chinese invention patent CN109590333A discloses a method for preparing thin-walled steel pipes using a small billet. The method involves using a continuously cast billet with a diameter of 155-230 mm to perform jacking and sizing treatment with a mandrel with a diameter of 145-220 mm, resulting in a thin-walled steel pipe with an outer diameter of 121-232 mm and a wall thickness of 4.5-8.0 mm. However, this patent struggles to achieve the required wall thickness of 3.00-5.00 mm and also fails to meet the ±0.3 mm wall thickness deviation requirement for seamless steel pipes used in power plant soot blowers.

[0005] Chinese invention patent CN111979382A discloses a large-diameter thin-walled seamless steel pipe and its preparation method. The preparation method includes: step S1, heating, piercing, rolling, and sizing the billet sequentially to obtain a sizing steel pipe; step S2, subjecting the sizing steel pipe to quenching, hot expansion, and tempering to obtain a large-diameter thin-walled seamless steel pipe. However, the hot expansion process used in this patent may lead to coarse metal grains due to high-temperature heating and plastic deformation, reducing the strength, toughness, and fatigue resistance of the material. This is especially significant for pipelines that need to withstand high pressure or dynamic loads. During the expansion of the thin-walled steel pipe, the difference in metal flow between the inner and outer layers is large, which can easily cause local excessive wall thickness or "wavy" thickness fluctuations, which are difficult to completely correct in subsequent processing.

[0006] Chinese invention patent CN116926401A discloses a rolling method for ODS ferritic thin-walled steel pipes. The method involves preparing an ODS ferritic tube billet using hot isostatic pressing or hot extrusion; heating the billet to 550-650℃ with a pass deformation controlled at 35-45% for multiple passes of high-deformation warm rolling, followed by vacuum annealing after each pass; then, controlling the pass deformation at 20-30% for multiple passes of low-deformation cold rolling; and finally, vacuum annealing to obtain the finished ODS ferritic thin-walled steel pipe. However, this patent combines warm rolling and cold rolling processes with high-temperature vacuum annealing, but it relies on high-precision mother tubes and specialized equipment, resulting in high technical barriers and high costs, making it difficult to popularize.

[0007] Chinese invention patent CN101497960A discloses a high-strength anti-collision tube for automobiles and its manufacturing method. It uses a piercing + cold rolling or cold drawing process to produce a steel tube with a maximum wall thickness of 2.5mm. In existing cold working processes, while cold rolling can achieve a wall thickness reduction rate of over 80% and correct uneven wall thickness, cyclic rolling easily produces bamboo-like patterns, and fluctuations in material feeding lead to localized uneven wall thickness. Cold drawing, while eliminating bamboo-like patterns and highly efficient, has weak ability to correct uneven wall thickness in the main tube, and its deformation is limited (≤30%), making it unable to independently achieve high-precision wall thickness reduction. Both methods require multiple passes of annealing and pickling, resulting in long production cycles and high energy consumption. Furthermore, the cold work hardening tendency of T91 steel exacerbates the process complexity.

[0008] For high-alloy steel tubes like T91 used in power plant soot blowers, which are difficult to deform, the outer diameter and wall thickness accuracy exceed the limits of hot rolling, making direct hot rolling into tubes difficult. Cold rolling can achieve a large amount of deformation for difficult-to-deform metals, and has a strong effect on correcting the wall thickness of the parent tube during deformation, significantly reducing the wall thickness unevenness of steel tubes. However, the cyclic rolling of cold-rolled tubes produces bamboo-like patterns, and the wall thickness becomes unstable during the feeding process, resulting in point-like thinning of the wall, which limits the accuracy and quality of cold-rolled products. Single cold drawing has high production efficiency (compared to cold rolling) and can significantly reduce bamboo-like patterns and point-like thinning of the wall during cold rolling deformation. However, its ability to correct the wall thickness unevenness of the parent tube is weak, and it cannot perform large-scale deformation to reduce the diameter and wall thickness for difficult-to-deform metals. Under the existing single-process (hot rolling / cold rolling / cold drawing) system, the dimensional accuracy of steel tubes cannot be guaranteed, and it is difficult to balance surface quality and production efficiency, which cannot meet the requirements for seamless steel tubes used in power plant soot blowers.

[0009] Therefore, to solve the above problems, the present invention proposes a method for high-precision T91 thin-walled steel pipe based on cold rolling and cold drawing synergistic deformation, which takes into account high-precision wall reduction, outer diameter control and surface quality optimization, and becomes the key to breaking through industry bottlenecks and achieving large-scale and efficient production. Summary of the Invention

[0010] The purpose of this invention is to provide a method for producing high-precision T91 thin-walled steel pipes based on the coordinated deformation of cold rolling and cold drawing, so as to solve the problems mentioned in the background art.

[0011] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0012] A method for producing high-precision T91 thin-walled steel pipes based on the coordinated deformation of cold rolling and cold drawing includes the following steps:

[0013] Step 1: Hot rolling process is carried out on T91 round tube billet to obtain hot-rolled steel pipe with outer diameter of Φ114~232mm and wall thickness of 6~9mm;

[0014] Step 2: The hot-rolled steel pipe is subjected to a cold rolling process. During the process, the wall reduction accounts for 70-80% of the total wall reduction and the diameter reduction accounts for 80-90% of the total diameter reduction, thus obtaining a cold-rolled steel pipe.

[0015] Step 3: The cold-rolled steel pipe is subjected to a cold drawing process. During the process, the wall reduction accounts for 20-30% of the total wall reduction and the diameter reduction accounts for 10-20% of the total diameter reduction, thus obtaining a cold-drawn steel pipe.

[0016] Step 4: The cold-drawn steel pipe undergoes a heat treatment process, which includes normalizing and tempering to obtain a high-precision T91 thin-walled steel pipe.

[0017] Step 5: Inspect the dimensions and performance of the high-precision T91 thin-walled steel pipe to obtain the final product.

[0018] Ideally, the total wall reduction in steps 2 and 3 is 40-60%, and the total diameter reduction is 10-20%.

[0019] In a more optimized manner, the dimensional accuracy of the final product is as follows: the allowable deviation of the outer diameter D is ±0.55mm, the maximum value of the outer diameter out-of-roundness Dmax-Dmin is 1.10mm; the allowable deviation of the wall thickness S is ±0.30mm, and the maximum value of the wall thickness unevenness Smax-Smin is 0.60mm.

[0020] The final product has the following properties: yield strength Rt0.5≥415MPa, tensile strength Rm≥585MPa; elongation after fracture A≥20%; Brinell hardness 190~250HBW; and microstructure is uniform tempered martensite.

[0021] In a more optimized manner, step 1 includes the following steps in the hot rolling process: holding the T91 round tube billet at 1140~1260℃ for 1~3 hours; then, in a conical piercing mill, controlling the expansion rate at 5~15%, and the rolling angle and feed angle at 10~15° to obtain a rough tube; and then sandblasting and grinding the inner and outer surfaces of the rough tube to obtain a hot-rolled steel pipe.

[0022] In a more optimized manner, step 2 includes the following steps in the cold rolling process: the hot-rolled steel pipe is cold-rolled in 1-2 passes using a Pilger mill; pickling and annealing are performed before cold rolling, with the annealing temperature being 650-700℃ and the annealing time being 1-3 hours; and a cold-rolled steel pipe is obtained.

[0023] The specific pickling process is as follows: place the sample in pickling solution A and pickle at 60~65℃ for 3~5 minutes; transfer it to a 4~6g / L oxalic acid aqueous solution, activate it with acid at 40~45℃ for 60~80 seconds, wash with water, and dry with nitrogen.

[0024] The pickling solution A comprises the following components: 50-60 g / L sulfuric acid, 10-15 g / L hydrofluoric acid, 10-15 g / L phosphoric acid, 0.5-1 g / L sodium dodecylbenzenesulfonate, and the remainder is deionized water.

[0025] In a more optimized manner, step 3 includes the following steps in the cold drawing process: pickling, phosphating, and saponifying the surface of the cold-rolled steel pipe, placing it in a cold drawing mold, and performing 1 to 2 cold drawing passes to obtain the cold-drawn steel pipe.

[0026] In a more optimized manner, step 4 includes the following steps in the heat treatment process: the cold-drawn steel pipe is first subjected to normalizing treatment: held at 1040~1080℃ for 0.5~1 hour and air-cooled to room temperature; then tempering treatment is performed: held at 740~780℃ for 1.5~3 hours; to obtain high-precision T91 thin-walled steel pipe.

[0027] In a more optimized manner, a lubricant is used in the cold drawing process. The lubricant includes glass powder, modified molybdenum disulfide, sodium carbonate, and boric acid powder in a mass ratio of 1:0.1:0.1:0.05.

[0028] In a more optimized manner, the pickling process in the cold drawing process is as follows: the sample is placed in pickling solution B and pickled at 50-55°C for 5-7 minutes, followed by water washing and nitrogen drying; the pickling solution B comprises the following components: sulfuric acid at 30-40 g / L, hydrofluoric acid at 5-10 g / L, citric acid at 20-25 g / L, thiourea at 0.5-1 g / L, and the remainder being deionized water;

[0029] The specific phosphating process is as follows: place the sample in a phosphating solution and phosphate at 50-55°C for 15-30 minutes, then wash with water and dry with nitrogen. The phosphating solution comprises the following components: 15-20 g / L zinc dihydrogen phosphate, 2-5 g / L phosphoric acid, 2-5 g / L zinc calcium phosphate, 0.1-0.2 g / L modified molybdenum disulfide, 0.05-0.1 g / L polyethylene glycol-4000, and the remainder is deionized water.

[0030] The specific process of the saponification treatment is as follows: place the sample in a saponification solution, saponify it at 70~90℃ for 3~10 minutes, and then dry it; the saponification solution includes the following components: 10~15wt% sodium stearate, 1~3g / L sodium hydroxide, 5~10g / L triethanolamine, and 0.02~0.05g / L modified molybdenum disulfide.

[0031] In a more optimized manner, the preparation method of the modified molybdenum disulfide is as follows: a portion of dopamine is dissolved in Tris-buffered solution, then nano-zirconium phosphate and flake molybdenum disulfide are added, ultrasonically dispersed evenly, then the remaining dopamine is added, stirred at room temperature for 24 hours, centrifuged, washed, and freeze-dried to obtain modified molybdenum disulfide; the mass ratio of dopamine, nano-zirconium phosphate, and flake molybdenum disulfide is 2:1:1.

[0032] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0033] 1. This application utilizes a synergistic deformation mechanism involving hot rolling, cold rolling, and cold drawing. By controlling the proportional distribution of wall and diameter reduction in each process, it overcomes the deformation limits of a single process. In the cold rolling process, large deformation rapidly eliminates uneven wall thickness. In the cold drawing process, the outer diameter is precisely corrected, and defects such as bamboo-like patterns caused by cold rolling are eliminated. Through synergistic control, the difficulty of achieving high-precision dimensional control of T91 thin-walled steel pipes using traditional single-process methods (hot rolling / cold rolling / cold drawing) is resolved.

[0034] 2. Compared with a single process, this application combines multiple processes to synergistically improve the ability to reduce wall thickness and control wall thickness unevenness; it effectively promotes a significant improvement in surface quality and overall yield, enabling it to meet the application requirements of lightweight and thin-walled T91 seamless steel pipes for power plant soot blowers.

[0035] 3. This application effectively avoids surface defects and affects quality by using differentiated pickling processes in the cold rolling and cold drawing processes. In the cold rolling process, since there is no subsequent lubricating substrate, phosphoric acid is introduced while removing oxide scale to promote the formation of phosphating film, and oxalic acid is used to activate it and promote uniformity, thereby increasing rolling lubricity, ensuring cold rolling quality, and suppressing surface defects. In the cold drawing process, thiourea is introduced in the pickling process to suppress cold drawing defects.

[0036] Meanwhile, in order to ensure the quality of cold drawing, modified molybdenum disulfide was introduced. The introduction of this substance not only has the property of reducing friction, but also acts as a phosphating accelerator in the phosphating process, which can improve the friction resistance of the phosphating coating, thereby improving the surface quality and overall performance defects in the cold drawing process.

[0037] Furthermore, a specially formulated lubricant was used to improve the quality of cold-drawing steel pipes. Glass powder softens at the localized high temperatures during cold drawing to form a viscous glass film, isolating the mold from the steel pipe surface and reducing direct contact friction. Molten glass fills micro-cracks on the steel pipe surface, reducing surface defects caused by stress concentration. Modified molybdenum disulfide acts as a friction reducer, providing extreme pressure lubrication, reducing adhesive wear, and preventing material transfer between the mold and the steel pipe. Sodium carbonate neutralizes acidic contaminants generated during cold drawing (such as residual cutting fluid and oxidation products), maintaining the chemical stability of the lubricant. The introduction of boric acid forms a low-temperature eutectic with the glass powder (such as borosilicate glass), adapting to the localized high temperatures during cold drawing. Simultaneously, sodium carbonate provides an alkaline environment to neutralize acidic contaminants, while boric acid buffers the pH, preventing excessive alkalinity from causing corrosion on the steel pipe surface and inhibiting excessive oxidation of the newly formed metal surface. Through this comprehensive regulation, low friction and high surface quality are achieved during the cold drawing of steel pipes. Attached Figure Description

[0038] Figure 1 The image shows the microstructure of the high-precision T91 thin-walled steel pipe in Example 1 at 500x magnification.

[0039] Figure 2 This is a microstructure image of the high-precision T91 thin-walled steel pipe in Example 2, magnified 500 times. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] In the following embodiments, the parts are by weight; it should be noted that there are no special restrictions on the purchase manufacturers of all the raw materials involved in this invention. Exemplary examples include: nano zirconium phosphate with a mesh size of 200 mesh; flake molybdenum disulfide with a specification of 200nm; and boric acid powder, which is anhydrous boric acid, white powder, and brand name and model name Xinmingtai.

[0042] The modified molybdenum disulfide was prepared by dissolving 0.5 parts of dopamine in 20 parts of Tris-buffered saline at pH 8.5, then adding 0.5 parts of nano-zirconium phosphate and 0.5 parts of flake molybdenum disulfide, ultrasonically dispersing them evenly, then adding another 0.5 parts of dopamine, stirring at room temperature for 24 hours, centrifuging, washing, and freeze-drying to obtain the modified molybdenum disulfide.

[0043] Example 1: A method for producing high-precision T91 thin-walled steel pipes based on the coordinated deformation of cold rolling and cold drawing, comprising the following steps:

[0044] Step 1: Heat the T91 round tube billet with a diameter of Φ210mm to 1150℃ and hold for 2.5 hours; then use a conical piercing mill to control the expansion rate of 10%, the rolling angle and the feed angle of 12°, and roll continuously to obtain a sizing tube with a diameter of Φ159mm×6.8mm; perform sandblasting and grinding on the inner and outer surfaces of the tube to ensure that there are no defects such as oxide scale, cracks, folds, peeling, scratches, holes, or unevenness on the inner and outer surfaces of the tube, and obtain a hot-rolled steel pipe.

[0045] Step 2: The hot-rolled steel pipe is cold-rolled in one pass using a Pilger mill; the wall reduction in the cold rolling process accounts for 70% of the total wall reduction and the diameter reduction accounts for 80% of the total diameter reduction. After cold rolling, a tube with a specification of Φ144×4.5mm is obtained. Pickling and annealing are performed before cold rolling. The annealing treatment is performed at 700℃ for 2 hours to obtain the cold-rolled steel pipe.

[0046] The specific pickling process is as follows: place the solution in pickling solution A and pickle at 60°C for 5 minutes; transfer to a 5 g / L oxalic acid aqueous solution, activate with acid at 40°C for 60 seconds, wash with water, and dry with nitrogen.

[0047] Pickling solution A comprises the following components: 55 g / L sulfuric acid, 12 g / L hydrofluoric acid, 13 g / L phosphoric acid, 0.5 g / L sodium dodecylbenzenesulfonate, and the remainder is deionized water;

[0048] Step 3: The surface of the cold-rolled steel pipe is pickled, phosphated, and saponified; it is placed in a cold drawing die, ensuring good lubrication of the die, using a lubricant, and cold drawing is carried out in one pass. The wall reduction in the cold drawing process accounts for 30% of the total wall reduction, and the diameter reduction accounts for 20% of the total diameter reduction; after cold drawing, a cold-drawn steel pipe with a specification of Φ140×3.5mm is obtained.

[0049] The specific pickling process is as follows: place the sample in pickling solution B, pickle at 50°C for 6 minutes, wash with water, and dry with nitrogen gas; the pickling solution B includes the following components: 35 g / L sulfuric acid, 7 g / L hydrofluoric acid, 23 g / L citric acid, 0.8 g / L thiourea, and the remainder is deionized water;

[0050] The specific phosphating process is as follows: place the sample in a phosphating solution, phosphate at 55°C for 20 minutes, wash with water, and dry with nitrogen. The phosphating solution comprises the following components: 18 g / L zinc dihydrogen phosphate, 4 g / L phosphoric acid, 4 g / L zinc calcium phosphate, 0.1 g / L modified molybdenum disulfide, 0.05 g / L polyethylene glycol-4000, and the remainder is deionized water.

[0051] The specific process of saponification is as follows: place the sample in a saponification solution, saponify it at 85°C for 5 minutes, and then dry it; the saponification solution includes the following components: 12wt% sodium stearate, 2g / L sodium hydroxide, 6g / L triethanolamine, and 0.02g / L modified molybdenum disulfide;

[0052] The lubricant comprises glass powder, modified molybdenum disulfide, sodium carbonate, and boric acid powder in a mass ratio of 1:0.1:0.1:0.05.

[0053] Step 4: First, normalize the cold-drawn steel pipe: hold it at 1040℃ for 1 hour and air cool it to room temperature; then temper it: hold it at 780℃ for 2 hours; to obtain a high-precision T91 thin-walled steel pipe.

[0054] Step 5: The high-precision T91 thin-walled steel pipe inspection process includes product size and performance inspection to obtain the final product.

[0055] In this embodiment, the high-precision T91 thin-walled steel pipe contains the following components by mass percentage: C: 0.10%, Si: 0.25%, Mn: 0.40%, P: 0.014%, S: 0.0020%, Cr: 8.54%, Ni: 0.20%, Mo: 0.90%, V: 0.20%, Ti: 0.0014%, Nb: 0.069%, B: 0.0003%, Zr: 0.0013%, N: 0.049%.

[0056] Example 2: A method for high-precision T91 thin-walled steel pipe based on cold rolling and cold drawing synergistic deformation, comprising the following steps:

[0057] Step 1: Heat the T91 round tube billet with a diameter of Φ310mm to 1180℃ and hold for 3 hours; then use a conical piercing mill to control the expansion rate of 10%, the rolling angle and the feed angle of 12°, and continuously roll to obtain a Φ219mm×8mm tube; perform sandblasting and grinding on the inner and outer surfaces of the tube to ensure that there are no defects such as oxide scale, cracks, folds, peeling, scratches, holes, or unevenness on the inner and outer surfaces of the tube, and obtain a hot-rolled steel pipe.

[0058] Step 2: The hot-rolled steel pipe is cold-rolled in one pass using a Pilger mill; the wall reduction in the cold rolling process accounts for 75% of the total wall reduction and the diameter reduction accounts for 82% of the total diameter reduction. After cold rolling, a tube with a specification of Φ187×4.85mm is obtained. Pickling and annealing are performed before cold rolling. The annealing treatment is performed at 700℃ for 2 hours to obtain the cold-rolled steel pipe.

[0059] The specific pickling process is as follows: place the solution in pickling solution A and pickle at 60°C for 5 minutes; transfer to a 5 g / L oxalic acid aqueous solution, activate with acid at 40°C for 60 seconds, wash with water, and dry with nitrogen.

[0060] Pickling solution A comprises the following components: 55 g / L sulfuric acid, 12 g / L hydrofluoric acid, 13 g / L phosphoric acid, 0.5 g / L sodium dodecylbenzenesulfonate, and the remainder is deionized water;

[0061] Step 3: Pickling, phosphating, and saponification are performed on the surface of the cold-rolled steel pipe; it is placed in a cold drawing die, ensuring good lubrication of the cold drawing die, using a lubricant, and cold drawing is carried out in one pass. The wall reduction in the cold drawing process accounts for 25% of the total wall reduction, and the diameter reduction accounts for 18% of the total diameter reduction; after cold drawing, a cold-drawn steel pipe with a specification of Φ180×3.8mm is obtained.

[0062] The specific pickling process is as follows: place the sample in pickling solution B, pickle at 50°C for 6 minutes, wash with water, and dry with nitrogen gas; the pickling solution B includes the following components: 35 g / L sulfuric acid, 7 g / L hydrofluoric acid, 23 g / L citric acid, 0.8 g / L thiourea, and the remainder is deionized water;

[0063] The specific phosphating process is as follows: place the sample in a phosphating solution, phosphate at 55°C for 20 minutes, wash with water, and dry with nitrogen. The phosphating solution comprises the following components: 18 g / L zinc dihydrogen phosphate, 4 g / L phosphoric acid, 4 g / L zinc calcium phosphate, 0.1 g / L modified molybdenum disulfide, 0.05 g / L polyethylene glycol-4000, and the remainder is deionized water.

[0064] The specific process of saponification is as follows: place the sample in a saponification solution, saponify it at 85°C for 5 minutes, and then dry it; the saponification solution includes the following components: 12wt% sodium stearate, 2g / L sodium hydroxide, 6g / L triethanolamine, and 0.02g / L modified molybdenum disulfide;

[0065] The lubricant comprises glass powder, modified molybdenum disulfide, sodium carbonate, and boric acid powder in a mass ratio of 1:0.1:0.1:0.05.

[0066] Step 4: First, normalize the cold-drawn steel pipe: hold it at 1050℃ for 1 hour and air cool it to room temperature; then temper it: hold it at 750℃ for 2 hours; to obtain a high-precision T91 thin-walled steel pipe.

[0067] Step 5: The high-precision T91 thin-walled steel pipe inspection process includes product size and performance inspection to obtain the final product.

[0068] In this embodiment, the high-precision T91 thin-walled steel pipe contains the following components by mass percentage: C: 0.10%, Si: 0.26%, Mn: 0.39%, P: 0.014%, S: 0.0020%, Cr: 8.51%, Ni: 0.15%, Mo: 0.92%, V: 0.22%, Ti: 0.0013%, Nb: 0.071%, B: 0.0004%, Zr: 0.0012%, N: 0.046%.

[0069] Comparative Example 1: Based on Example 1, without the use of lubricant, otherwise the same as Example 1.

[0070] Comparative Example 2: Based on Example 1, boric acid was not introduced into the lubricant. Specifically, the lubricant included glass powder, modified molybdenum disulfide, and sodium carbonate in a mass ratio of 1:0.1:0.1; the rest was the same as in Example 1.

[0071] Comparative Example 3: Based on Example 1, the amount of boric acid introduced into the lubricant was increased. Specifically, the lubricant included glass powder, modified molybdenum disulfide, sodium carbonate, and boric acid powder in a mass ratio of 1:0.1:0.1:0.1; the rest was the same as in Example 1.

[0072] Performance Test 1: The high-precision T91 thin-walled steel pipes prepared in Examples 1 and 2 were subjected to multi-point measurements of dimensional accuracy, mechanical properties, and microstructure. Longitudinal tensile tests were conducted according to ASTM E8 / E8M, hardness was tested according to ASTM E10, and microstructure was examined according to GB / T 13298. The obtained data are shown in Table 1.

[0073] Table 1:

[0074]

[0075] Conclusion: Based on the data in Table 1 and Figure 1 and Figure 2It can be seen that the high-precision T91 thin-walled steel pipe prepared in this application achieves ultra-high precision control: wall thickness deviation ±0.3mm, outer diameter deviation ±0.55mm, outer diameter out-of-roundness ≤1.10mm, wall thickness unevenness ≤0.60mm, and mechanical properties meet ASTM standards (yield strength ≥415MPa, tensile strength ≥585MPa), solving the problem of lightweighting and thinning of T91 steel pipes used in power plant soot blowers.

[0076] Performance Test 2: The high-precision T91 thin-walled steel pipes obtained from Comparative Examples 1-3 were subjected to relevant wall thickness deviation and surface quality evaluation (smooth surface: smooth to the touch, no obvious processing marks; relatively smooth surface: smooth to the touch, with slight processing marks; fair surface: no sharp bumps or depressions, but visible processing lines). The data obtained are shown in Table 2.

[0077] Table 2:

[0078]

[0079] Conclusion: The data in Table 2 show that in Comparative Examples 1 and 2, the absence of lubricant increases wall thickness deviation and decreases surface quality; the absence of boric acid increases drawing defects; and the excessive introduction of boric acid produces non-lubricating products, weakens the lamellar slip properties of MoS2, and results in cold drawing defects and decreased surface quality.

[0080] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for producing high-precision thin-walled steel pipes based on the coordinated deformation of cold rolling and cold drawing, characterized in that: Includes the following steps: Step 1: Hot rolling process is carried out on T91 round tube billet to obtain hot-rolled steel pipe with outer diameter of Φ114~232mm and wall thickness of 6~9mm; Step 2: The hot-rolled steel pipe is cold-rolled in 1-2 passes using a Pilger mill; before cold rolling, pickling and annealing are performed, with the annealing temperature at 650-700℃ and the annealing time at 1-3 hours; cold-rolled steel pipe is obtained; during the process, the wall reduction accounts for 70-80% of the total wall reduction and the diameter reduction accounts for 80-90% of the total diameter reduction, thus obtaining the cold-rolled steel pipe; Step 3: The surface of the cold-rolled steel pipe is pickled, phosphated, and saponified. It is then placed in a cold-drawing die and cold-drawn in 1-2 passes to obtain the cold-drawn steel pipe. During the process, the wall reduction accounts for 20-30% of the total wall reduction, and the diameter reduction accounts for 10-20% of the total diameter reduction. Step 4: The cold-drawn steel pipe undergoes a heat treatment process, which includes normalizing and tempering to obtain a high-precision T91 thin-walled steel pipe. Step 5: Inspect the dimensions and performance of the high-precision T91 thin-walled steel pipes to obtain the final product; In the cold rolling process, the pickling process is as follows: place the sample in pickling solution A and pickle at 60~65℃ for 3~5 minutes; transfer it to an oxalic acid aqueous solution of 4~6g / L, activate it with acid at 40~45℃ for 60~80 seconds, wash with water, and dry with nitrogen. The pickling solution A comprises the following components: 50-60 g / L sulfuric acid, 10-15 g / L hydrofluoric acid, 10-15 g / L phosphoric acid, 0.5-1 g / L sodium dodecylbenzenesulfonate, and the remainder is deionized water; In the cold drawing process, a lubricant is used, which includes glass powder, modified molybdenum disulfide, sodium carbonate, and boric acid powder in a mass ratio of 1:0.1:0.1:0.

05. The specific pickling process is as follows: place the sample in pickling solution B, pickle at 50~55℃ for 5~7 minutes, rinse with water, and dry with nitrogen. The pickling solution B comprises the following components: 30-40 g / L sulfuric acid, 5-10 g / L hydrofluoric acid, 20-25 g / L citric acid, 0.5-1 g / L thiourea, and the remainder is deionized water; The specific phosphating process is as follows: place the sample in a phosphating solution and phosphate at 50-55°C for 15-30 minutes, then wash with water and dry with nitrogen. The phosphating solution comprises the following components: 15-20 g / L zinc dihydrogen phosphate, 2-5 g / L phosphoric acid, 2-5 g / L zinc calcium phosphate, 0.1-0.2 g / L modified molybdenum disulfide, 0.05-0.1 g / L polyethylene glycol-4000, and the remainder is deionized water. The specific process of saponification is as follows: place the sample in a saponification solution and saponify it at 70~90℃ for 3~10 minutes, then dry it; the saponification solution includes the following components: 10~15wt% sodium stearate, 1~3g / L sodium hydroxide, 5~10g / L triethanolamine, and 0.02~0.05g / L modified molybdenum disulfide.

2. The method for producing high-precision thin-walled steel pipes based on the coordinated deformation of cold rolling and cold drawing according to claim 1, characterized in that: The total wall reduction in steps 2 and 3 is 40-60%, and the total diameter reduction is 10-20%.

3. The method for producing high-precision thin-walled steel pipes based on the coordinated deformation of cold rolling and cold drawing according to claim 1, characterized in that: The dimensional accuracy of the final product is as follows: the allowable deviation of outer diameter D is ±0.55mm, the maximum value of outer diameter out-of-roundness Dmax-Dmin is 1.10mm; the allowable deviation of wall thickness S is ±0.30mm, and the maximum value of wall thickness unevenness Smax-Smin is 0.60mm. The final product has the following properties: yield strength Rt0.5≥415MPa, tensile strength Rm≥585MPa; elongation after fracture A≥20%; Brinell hardness 190~250HBW; and microstructure is uniform tempered martensite.

4. The method for producing high-precision thin-walled steel pipes based on the coordinated deformation of cold rolling and cold drawing according to claim 1, characterized in that: In step 1, the hot rolling process includes the following steps: holding the T91 round tube billet at 1140~1260℃ for 1~3 hours; then, in a conical piercing mill, controlling the expansion rate at 5~15%, and the rolling angle and feed angle at 10~15° to obtain a rough tube; and then sandblasting and grinding the inner and outer surfaces to obtain a hot-rolled steel pipe.

5. The method for producing high-precision thin-walled steel pipes based on the coordinated deformation of cold rolling and cold drawing according to claim 1, characterized in that: In step 4, the heat treatment process includes the following steps: the cold-drawn steel pipe is first normalized: held at 1040~1080℃ for 0.5~1 hour and air-cooled to room temperature; then tempered: held at 740~780℃ for 1.5~3 hours; to obtain high-precision T91 thin-walled steel pipe.

6. The method for producing high-precision thin-walled steel pipes based on the coordinated deformation of cold rolling and cold drawing according to claim 1, characterized in that: The modified molybdenum disulfide was prepared by dissolving a portion of dopamine in Tris-buffered saline, then adding nano-zirconium phosphate and flake molybdenum disulfide, ultrasonically dispersing the mixture evenly, then adding the remaining dopamine, stirring at room temperature for 24 hours, centrifuging, washing, and freeze-drying to obtain modified molybdenum disulfide; the mass ratio of dopamine, nano-zirconium phosphate, and flake molybdenum disulfide was 2:1:1.

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