Method for cooperatively deforming high-precision thin-wall steel pipe based on cold rolling and cold drawing

Abstract

The invention discloses a method for cooperatively deforming a high-precision thin-wall steel pipe based on cold rolling and cold drawing, and relates to the technical field of metal materials. Comprising the following steps that a T91 round pipe blank is sequentially subjected to a hot rolling procedure, a cold rolling procedure, a cold drawing procedure and a heat treatment procedure, and the high-precision T91 thin-wall steel pipe is obtained; and carrying out product size and performance inspection to obtain a final product. By optimizing and limiting the process in each procedure, the wall thickness reduction capacity of the steel pipe is effectively improved, the wall thickness unevenness control is realized, the surface quality is enhanced, the improvement of the comprehensive yield is promoted, and the application scene requirements of light weight and thin wall of the T91 seamless steel pipe for the soot blower of the power plant are met.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a method for cooperatively deforming a high-precision T91 thin-walled steel pipe based on cold rolling and cold drawing. Background Art

[0002] A sootblower in a power plant is a key device used to remove dust from the surface of equipment such as boilers and heat exchangers. On the one hand, its working environment involves high temperature, high pressure, and corrosive media, requiring the seamless steel pipes of its 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 supporting structure and improve the flexibility and responsiveness of equipment operation, the steel pipes need to be lightweight. Among them, ASME SA-213 T91 seamless steel pipes meet the requirements of their service environment. However, the demand for lightweight and thin-walled steel pipes places higher demands on dimensional accuracy. Taking a Φ140×3.5mm steel pipe as an example, the allowable deviation of the steel pipe's outer diameter D (the maximum allowable deviation between the actual outer diameter and the nominal outer diameter) is ±0.55mm, and 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 between the actual wall thickness and the nominal wall thickness) is ±0.30mm, and the maximum value of the wall thickness unevenness Smax-Smin (the difference between the maximum and minimum wall thickness on the same cross-section of the steel pipe) is 0.60mm. This far exceeds the conventional ASME SA213 standard (taking a Φ140×3.5mm steel pipe as an example, the allowable deviation range for outer diameter D is -1.20 to 0.40mm, with no requirements for outer diameter out-of-roundness; the allowable deviation range for wall thickness S is 0 to 1.16mm, with no requirements for wall thickness unevenness). Currently, due to equipment limitations, traditional hot-rolling processes for T91 thin-walled steel pipes only allow a minimum wall thickness of 6mm with wide tolerances, failing to meet thin-wall requirements. Currently, only a few companies utilize a "hot-rolled mother pipe + cold-forming" process to supply this product, but this relies on high-precision mother pipes and specialized equipment, resulting in high technical barriers and high costs, making it difficult to popularize.

[0003] In the existing technology, there are already some invention patents for solving the problem of achieving large-scale and efficient production of high-precision thin-walled steel pipes; the relevant ones are as follows: Chinese invention patent CN109590333A discloses a pipe-jacking method for producing thin-walled steel pipes using small billets. This method involves using a 145-220mm diameter mandrel to perform pipe-jacking and sizing on continuously cast billets with diameters of 155-230mm. The resulting thin-walled steel pipes have outer diameters of 121-232mm and wall thicknesses of 4.5-8.0mm. However, this patent fails to achieve the minimum wall thickness requirement of 3.00-5.00mm, and also fails to meet the ±0.3mm wall thickness tolerance requirement for seamless steel pipes used in power plant sootblowers.

[0004] Chinese invention patent number CN111979382A discloses a large-diameter, thin-walled seamless steel pipe and its preparation method. The preparation method comprises: step S1, sequentially heating, perforating, rolling, and sizing a tube blank to obtain a sized steel pipe; and step S2, subjecting the sized steel pipe to a quenching, thermal expansion, and tempering process to obtain a large-diameter, thin-walled seamless steel pipe. However, the high-temperature heating and plastic deformation of the thermal expansion process employed in this patent may result in coarsening of the metal grains, reducing the material's strength, toughness, and fatigue resistance. This is particularly significant for pipes subject to high pressure or dynamic loads. When the thin-walled steel pipe is expanded, the metal flow difference between the inner and outer layers is significant, which can easily lead to localized excessive wall thickness or "wavy" thickness fluctuations, making it difficult to fully correct in subsequent processing.

[0005] Chinese invention patent CN116926401A discloses a rolling method for ODS ferrite thin-walled steel pipes. The method involves producing an ODS ferrite tube blank using hot isostatic pressing or hot extrusion. The blank is then heated to 550-650°C, with a deformation per pass controlled at 35-45%, and subjected to multiple passes of warm rolling with large deformations. Each warm rolling pass is followed by vacuum annealing. The resulting ODS ferrite thin-walled steel pipe is then cold rolled with a deformation per pass controlled at 20-30%, followed by vacuum annealing. However, the patent combines warm and cold rolling processes with a high-temperature vacuum annealing process, which relies on high-precision mother pipes and specialized equipment. This method presents a high technical barrier and is expensive, making it difficult to commercialize.

[0006] Chinese invention patent CN101497960A discloses a high-strength automotive anti-collision tube and its manufacturing method. The tube is produced using a perforation followed by cold rolling or cold drawing process, resulting in a maximum wall thickness of 2.5mm. Among existing cold working processes, cold rolling can achieve a wall reduction rate of over 80% per pass and correct uneven wall thickness, but cyclical rolling can easily produce bamboo knots, and feeding fluctuations can lead to localized uneven wall thickness. Cold drawing, while highly efficient, eliminates bamboo knots, but has limited correction capabilities for uneven wall thickness in the parent tube, resulting in a limited deformation range (≤30%) and inability to independently achieve high-precision wall reduction. Both processes require multiple intermediate treatments such as 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.

[0007] For high-alloy tubes like T91 used in power plant sootblowers, the outer diameter and wall thickness accuracy of these difficult-to-deform metals exceeds the limits of hot rolling, making direct hot rolling difficult. Cold rolling can achieve significant deformation for these difficult-to-deform metals, effectively correcting the wall thickness of the parent tube during deformation and significantly reducing wall thickness unevenness. However, cold rolling can produce bamboo marks during the rolling cycle, leading to unstable wall thickness during the loading process and the appearance of thin spots, which limit the precision and quality of the cold-rolled product. Single cold drawing offers high production efficiency (compared to cold rolling) and can significantly reduce bamboo marks and thin spots during cold rolling deformation. However, it has limited correction capabilities for uneven wall thickness in the parent tube and cannot achieve large diameter and wall reductions for difficult-to-deform metals. The existing single-process (hot rolling / cold rolling / cold drawing) system cannot guarantee the dimensional accuracy of steel pipes, making it difficult to balance surface quality and production efficiency, thus failing to meet the requirements for seamless steel pipes used in power plant sootblowers.

[0008] 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 coordinated 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 realizing large-scale and efficient production. Summary of the Invention

[0009] The object of the present 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 raised in the above-mentioned background technology.

[0010] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for high-precision T91 thin-walled steel pipe based on cold rolling and cold drawing collaborative deformation, comprising the following steps: Step 1: The T91 round tube billet is subjected to a hot rolling process to obtain a hot-rolled steel tube with an outer diameter of Φ114~232mm and a wall thickness range of 6~9mm; 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 to obtain a cold-rolled steel pipe; 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 to obtain a cold-drawn steel pipe; Step 4: The cold drawn steel pipe is subjected to a heat treatment process, during which: normalizing treatment is first performed, and then tempering treatment is performed to obtain a high-precision T91 thin-walled steel pipe; Step 5: Test the product size and performance of the high-precision T91 thin-walled steel pipe to obtain the final product.

[0011] More optimally, the total wall reduction in step 2 and step 3 is 40-60%, and the total diameter reduction is 10-20%.

[0012] More optimally, the dimensional accuracy of the final product is: the allowable deviation of the outer diameter D is ±0.55mm, and the maximum value of the outer diameter non-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; The properties of the final product are: yield strength Rt0.5≥415MPa, tensile strength Rm≥585MPa; elongation after fracture A≥20%; Brinell hardness 190~250HBW; and microstructure of uniform tempered martensite.

[0013] More optimally, in step 1, the hot rolling process includes the following steps: keeping the T91 round tube billet at 1140~1260℃ for 1~3 hours; then controlling the expansion rate to 5~15% and the rolling angle and feed angle to 10~15° in a tapered piercing mill to obtain a rough tube; sandblasting and grinding the inner and outer surfaces to obtain a hot-rolled steel pipe.

[0014] Preferably, in step 2, the cold rolling process comprises the following steps: cold rolling the hot-rolled steel pipe using a pilger mill for 1 to 2 passes; pickling and annealing the hot-rolled steel pipe before cold rolling, wherein the annealing temperature is 650 to 700° C. and the annealing time is 1 to 3 hours; and obtaining the cold-rolled steel pipe; The specific process of pickling is as follows: placing in pickling solution A, pickling at 60-65°C for 3-5 minutes; transferring to 4-6 g / L oxalic acid aqueous solution, acid activation at 40-45°C for 60-80 seconds, washing with water, and drying with nitrogen; The pickling solution A comprises the following components: 50-60 g / L of sulfuric acid, 10-15 g / L of hydrofluoric acid, 10-15 g / L of phosphoric acid, 0.5-1 g / L of sodium dodecylbenzenesulfonate, and the remainder is deionized water.

[0015] More optimally, in step 3, the cold drawing process includes the following steps: pickling, phosphating, and saponifying the surface of the cold-rolled steel pipe, placing it in a cold drawing die, and performing 1 to 2 cold drawing passes to obtain a cold-drawn steel pipe.

[0016] More optimally, in step 4, the heat treatment process includes the following steps: first normalizing the cold-drawn steel pipe: keeping it at 1040~1080℃ for 0.5~1 hour, and air cooling it to room temperature; then tempering it: keeping it at 740~780℃ for 1.5~3 hours; and obtaining a high-precision T91 thin-walled steel pipe.

[0017] More optimally, in the cold drawing process, a lubricant is used, and 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.

[0018] More optimally, in the cold drawing process, the specific process of pickling is: placing in pickling solution B, pickling at 50-55° C. for 5-7 minutes, washing with water, and drying 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 rest is deionized water; The specific process of the phosphating is as follows: placing the sample in a phosphating solution, phosphating at 50-55° C. for 15-30 minutes, washing with water, and drying 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 calcium zinc 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 the saponification treatment is: placing in a saponification solution, saponifying at 70-90° C. for 3-10 minutes, and drying; 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.

[0019] More optimally, the preparation method of the modified molybdenum disulfide is: dissolving part of the dopamine in Tris-buffered saline, then adding nano-zirconium phosphate and flaky molybdenum disulfide, ultrasonically dispersing them evenly, then adding the remaining dopamine, stirring at room temperature for 24 hours, centrifugally washing, and freeze-drying to obtain modified molybdenum disulfide; the mass ratio of dopamine, nano-zirconium phosphate, and flaky molybdenum disulfide is 2:1:1.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. This application utilizes a collaborative deformation mechanism involving hot rolling, cold rolling, and cold drawing, exceeding the deformation limits of a single process by controlling the proportional distribution of wall and diameter reduction in each process. Large deformation in the cold rolling process rapidly eliminates uneven wall thickness, while the cold drawing process precisely corrects the outer diameter and eliminates defects such as bamboo grain caused by cold rolling. This coordinated control overcomes the difficulties of high-precision dimensional control of T91 thin-walled steel pipes, which is difficult to achieve using traditional single processes (hot rolling / cold rolling / cold drawing).

[0021] 2. Compared with a single process, this application combines multiple processes to synergistically improve the wall thickness thinning capability and the control of wall thickness unevenness; it effectively promotes a significant improvement in surface quality and an increase in the overall yield rate, so that it can meet the application requirements of lightweight and thin-walled T91 seamless steel pipes for soot blowers in power plants.

[0022] 3. This application effectively avoids surface defects that affect quality by using differentiated pickling processes during the cold rolling and cold drawing processes; in the cold rolling process, since there is no subsequent lubrication base, phosphoric acid is introduced while removing the oxide scale to promote the formation of the phosphate film, and oxalic acid is used to activate it and promote uniformity, thereby increasing rolling lubricity, ensuring cold rolling quality, and suppressing surface defects; and in the cold drawing process, thiourea is introduced in the pickling to suppress cold drawing defects.

[0023] At the same time, in order to ensure the quality of cold drawing, modified molybdenum disulfide is introduced; the introduction of this substance not only has friction reduction properties, 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 comprehensive performance defects during the cold drawing process; In addition, specially formulated lubricants are also used to improve the quality of cold drawing of steel pipes. Among them, glass powder can soften at the local high temperature of cold drawing to form a sticky glass film, isolating the mold from the steel pipe surface and reducing direct contact friction. Molten glass can fill microcracks on the surface of the steel pipe and reduce surface defects caused by stress concentration. Modified molybdenum disulfide is 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 pollutants (such as residual cutting fluid and oxidation products) generated during the cold drawing process to maintain the chemical stability of the lubricant. The introduction of boric acid can form a low-temperature eutectic (such as borosilicate glass) with glass powder to adapt to the local high temperature of cold drawing. At the same time, sodium carbonate provides an alkaline environment to neutralize acidic pollutants, while boric acid buffers the pH to prevent excessive alkalinity from causing corrosion on the steel pipe surface and inhibit excessive oxidation of the new metal surface. Comprehensive regulation in sequence can achieve low friction and high surface quality in cold drawing of steel pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a microstructure picture of the high-precision T91 thin-walled steel pipe in Example 1 at a magnification of 500 times; Figure 2 This is a microstructure picture of the high-precision T91 thin-walled steel pipe in Example 2 at a magnification of 500 times. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0026] In the following embodiments, parts are by mass; it should be noted that the purchase manufacturers of all raw materials involved in the present invention are not subject to any special restrictions, and illustratively include: the mesh size of nano zirconium phosphate is 200 mesh; the specification of flaky molybdenum disulfide is 200nm; the boric acid powder is anhydrous boric acid, white powder, and the brand model is Xinmingtai.

[0027] The preparation method of modified molybdenum disulfide is as follows: 0.5 parts of dopamine are dissolved in 20 parts of Tris-buffer with pH=8.5, and then 0.5 parts of nano zirconium phosphate and 0.5 parts of flaky molybdenum disulfide are added, ultrasonically dispersed evenly, and then 0.5 parts of dopamine are added. The mixture is stirred at room temperature for 24 hours, centrifuged and washed, and freeze-dried to obtain modified molybdenum disulfide.

[0028] Example 1: A method for high-precision T91 thin-walled steel pipe based on cold rolling and cold drawing collaborative deformation, comprising the following steps: Step 1: Heat the T91 round tube with a diameter of Φ210mm to 1150℃ and keep it warm for 2.5 hours; then use a tapered piercing machine to control the expansion rate to 10%, the rolling angle and the feed angle to 12°, and after continuous rolling, the diameter is set to Φ159mm×6.8mm. The inner and outer surfaces of the tube are sandblasted and ground to ensure that there are no defects such as oxide scale, cracks, folds, warping, scratches, holes, bumps, etc. on the inner and outer surfaces of the tube to obtain a hot-rolled steel tube.

[0029] Step 2: The hot-rolled steel pipe is subjected to one pass of cold rolling 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, and a rough pipe with a specification of Φ144×4.5mm is obtained after cold rolling; pickling and annealing treatment are performed before cold rolling, and the annealing treatment is performed at 700°C for 2 hours to obtain a cold-rolled steel pipe; The specific pickling process is as follows: place in pickling solution A, pickle at 60°C for 5 minutes; transfer to 5g / L oxalic acid aqueous solution, acid activate at 40°C for 60 seconds, wash with water, and blow dry with nitrogen; Pickling solution A includes the following components: 55 g / L sulfuric acid, 12 g / L hydrofluoric acid, 13 g / L phosphoric acid, 0.5 g / L sodium dodecylbenzene sulfonate, and the remainder is deionized water; Step 3: The surface of the cold-rolled steel pipe is pickled, phosphated, and saponified; placed in a cold drawing die, ensuring good lubrication of the cold drawing die, using lubricant, and performing one cold drawing. 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; The specific process of pickling is as follows: placing in pickling solution B, pickling at 50°C for 6 minutes, washing with water, and drying with nitrogen; the pickling solution B comprises the following components: 35g / L sulfuric acid, 7g / L hydrofluoric acid, 23g / L citric acid, 0.8g / L thiourea, and the remainder is deionized water; The specific process of phosphating is as follows: placing the sample in a phosphating solution, phosphating at 55° C. for 20 minutes, washing with water, and drying with nitrogen; the phosphating solution comprises the following components: 18 g / L zinc dihydrogen phosphate, 4 g / L phosphoric acid, 4 g / L calcium zinc phosphate, 0.1 g / L modified molybdenum disulfide, 0.05 g / L polyethylene glycol-4000, and the remainder is deionized water; The specific process of saponification treatment is as follows: placing in a saponification solution, saponifying at 85°C for 5 minutes, and drying; the saponification solution includes the following components: 12wt% sodium stearate, 2g / L sodium hydroxide, 6g / L triethanolamine, and 0.02g / L modified molybdenum disulfide; 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; Step 4: The cold-drawn steel pipe is first normalized: kept at 1040℃ for 1 hour and air-cooled to room temperature; then tempered: kept at 780℃ for 2 hours to obtain a high-precision T91 thin-walled steel pipe.

[0030] Step 5: Carry out the high-precision T91 thin-walled steel pipe inspection process, conduct product size and performance inspection, and obtain the final product.

[0031] In this embodiment, the high-precision T91 thin-walled steel pipe has 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%, and N: 0.049%.

[0032] Example 2: A method for high-precision T91 thin-walled steel pipe based on cold rolling and cold drawing collaborative deformation, comprising the following steps: Step 1: Heat the T91 round tube with a diameter of Φ310mm to 1180℃ and keep it warm for 3 hours; then use a tapered piercing machine to control the expansion rate to 10%, the rolling angle and the feed angle to 12°, and after continuous rolling, the diameter is set to Φ219mm×8mm. The inner and outer surfaces of the tube are sandblasted and ground to ensure that there are no defects such as oxide scale, cracks, folds, warping, scratches, holes, bumps, etc. on the inner and outer surfaces of the tube to obtain a hot-rolled steel tube.

[0033] Step 2: The hot-rolled steel pipe is subjected to one cold rolling process 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, and a rough pipe with a specification of Φ187×4.85mm is obtained after cold rolling; pickling and annealing treatment are performed before cold rolling, and the annealing treatment is annealing at 700°C for 2 hours to obtain a cold-rolled steel pipe; The specific pickling process is as follows: place in pickling solution A, pickle at 60°C for 5 minutes; transfer to 5g / L oxalic acid aqueous solution, acid activate at 40°C for 60 seconds, wash with water, and blow dry with nitrogen; Pickling solution A includes the following components: 55 g / L sulfuric acid, 12 g / L hydrofluoric acid, 13 g / L phosphoric acid, 0.5 g / L sodium dodecylbenzene sulfonate, and the remainder is deionized water; Step 3: The surface of the cold-rolled steel pipe is pickled, phosphated, and saponified; placed in a cold drawing die, ensuring good lubrication of the cold drawing die, using lubricant, and performing one cold drawing. 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; The specific process of pickling is as follows: placing in pickling solution B, pickling at 50°C for 6 minutes, washing with water, and drying with nitrogen; the pickling solution B comprises the following components: 35g / L sulfuric acid, 7g / L hydrofluoric acid, 23g / L citric acid, 0.8g / L thiourea, and the remainder is deionized water; The specific process of phosphating is as follows: placing the sample in a phosphating solution, phosphating at 55° C. for 20 minutes, washing with water, and drying with nitrogen; the phosphating solution comprises the following components: 18 g / L zinc dihydrogen phosphate, 4 g / L phosphoric acid, 4 g / L calcium zinc phosphate, 0.1 g / L modified molybdenum disulfide, 0.05 g / L polyethylene glycol-4000, and the remainder is deionized water; The specific process of saponification treatment is as follows: placing in a saponification solution, saponifying at 85°C for 5 minutes, and drying; the saponification solution includes the following components: 12wt% sodium stearate, 2g / L sodium hydroxide, 6g / L triethanolamine, and 0.02g / L modified molybdenum disulfide; 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; Step 4: The cold-drawn steel pipe is first normalized: kept at 1050℃ for 1 hour and air-cooled to room temperature; then tempered: kept at 750℃ for 2 hours to obtain a high-precision T91 thin-walled steel pipe.

[0034] Step 5: Carry out the high-precision T91 thin-walled steel pipe inspection process, conduct product size and performance inspection, and obtain the final product.

[0035] In this embodiment, the components of the high-precision T91 thin-walled steel pipe are as follows 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%, and N: 0.046%.

[0036] Comparative Example 1: Based on Example 1, no lubricant was used, and the rest was the same as Example 1.

[0037] Comparative Example 2: Based on Example 1, boric acid is not introduced into the lubricant. The specific adjustment is as follows: the lubricant includes glass powder, modified molybdenum disulfide, and sodium carbonate in a mass ratio of 1:0.1:0.1; the rest is the same as Example 1.

[0038] Comparative Example 3: Based on Example 1, the amount of boric acid introduced into the lubricant is increased, and the specific adjustment is as follows: the lubricant includes glass powder, modified molybdenum disulfide, sodium carbonate, and boric acid powder in a mass ratio of 1:0.1:0.1:0.1; the rest is the same as Example 1.

[0039] Performance Test 1: The high-precision T91 thin-walled steel pipes prepared in Example 1 and Example 2 were subjected to multi-point measurements of dimensional accuracy, mechanical properties, and microstructure. A longitudinal tensile test was performed according to ASTM E8 / E8M, a hardness test was performed according to ASTM E10, and a microstructure test was performed according to GB / T 13298. The obtained data are shown in Table 1: Table 1:

[0040] Conclusion: According to the data in Table 1 and Figure 1 and Figure 2 It 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 lightweight and thin-walled T91 steel pipes used in power plant sootblowers.

[0041] Performance Test 2: The high-precision T91 thin-walled steel pipes obtained in Comparative Examples 1 to 3 were evaluated for wall thickness deviation and surface quality (smooth surface: refers to a smooth feel with no obvious processing marks; relatively smooth surface: refers to a smooth feel with slight processing marks; general surface: refers to a surface with no sharp bumps but visible processing marks). The obtained data are shown in Table 2: Table 2:

[0042] Conclusion: From the data in Table 2, it can be seen that in comparative examples 1 and 2, when there is no lubricant, the wall thickness deviation increases and the surface quality decreases; when boric acid is not introduced, the defects in drawing increase; when too much boric acid is introduced, non-lubricating products will be produced, which will weaken the lamellar slip characteristics of MoS2, resulting in defects in cold drawing and a decrease in surface quality.

[0043] 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 embodied 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 illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A method for cooperatively deforming high-precision thin-walled steel pipes by cold rolling and cold drawing, characterized in that: The following steps are involved: Step 1: The T91 round tube billet is subjected to a hot rolling process to obtain a hot-rolled steel tube with an outer diameter of Φ114~232mm and a wall thickness range of 6~9mm; 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 to obtain a cold-rolled steel pipe; 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 to obtain a cold-drawn steel pipe; Step 4: The cold drawn steel pipe is subjected to a heat treatment process, during which: normalizing treatment is first performed, and then tempering treatment is performed to obtain a high-precision T91 thin-walled steel pipe; Step 5: Test the product size and performance of the high-precision T91 thin-walled steel pipe to obtain the final product.

2. The method for forming a high-precision thin-walled steel pipe based on 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 forming a high-precision thin-walled steel pipe based on 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 the outer diameter D is ±0.55mm, the maximum value of the outer diameter non-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; The properties of the final product are: yield strength Rt0.5≥415MPa, tensile strength Rm≥585MPa; elongation after fracture A≥20%; Brinell hardness 190~250HBW; and microstructure of uniform tempered martensite.

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

5. The method for forming a high-precision thin-walled steel pipe based on cold rolling and cold drawing according to claim 1, characterized in that: In step 2, the cold rolling process includes the following steps: cold rolling the hot-rolled steel pipe using a pilger mill for 1 to 2 passes; pickling and annealing before cold rolling, wherein the annealing temperature is 650 to 700° C. and the annealing time is 1 to 3 hours; and obtaining the cold-rolled steel pipe; The specific process of pickling is as follows: placing in pickling solution A, pickling at 60-65°C for 3-5 minutes; transferring to 4-6 g / L oxalic acid aqueous solution, acid activation at 40-45°C for 60-80 seconds, washing with water, and drying with nitrogen; The pickling solution A comprises the following components: 50-60 g / L of sulfuric acid, 10-15 g / L of hydrofluoric acid, 10-15 g / L of phosphoric acid, 0.5-1 g / L of sodium dodecylbenzenesulfonate, and the remainder is deionized water.

6. The method for forming a high-precision thin-walled steel pipe based on cold rolling and cold drawing coordination according to claim 1, characterized in that: In step 3, the cold drawing process includes the following steps: pickling, phosphating, and saponifying the surface of the cold-rolled steel pipe, placing it in a cold drawing die, and performing 1 to 2 cold drawing passes to obtain a cold-drawn steel pipe.

7. The method for forming a high-precision thin-walled steel pipe based on cold rolling and cold drawing coordination according to claim 1, characterized in that: In step 4, the heat treatment process includes the following steps: first normalizing the cold-drawn steel pipe: keeping it at 1040-1080°C for 0.5-1 hour, and air cooling it to room temperature; then tempering it: keeping it at 740-780°C for 1.5-3 hours; to obtain a high-precision T91 thin-walled steel pipe.

8. The method for forming a high-precision thin-walled steel pipe based on cold rolling and cold drawing coordination according to claim 6, characterized in that: In the cold drawing process, a lubricant is used, and 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.

9. The method for forming a high-precision thin-walled steel pipe based on cold rolling and cold drawing coordination according to claim 6, characterized in that: In the cold drawing process, the specific process of pickling is as follows: placing in pickling solution B, pickling at 50-55°C for 5-7 minutes, washing with water, and drying 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 rest is deionized water; The specific process of the phosphating is as follows: placing the sample in a phosphating solution, phosphating at 50-55° C. for 15-30 minutes, washing with water, and drying 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 calcium zinc 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 the saponification treatment is: placing in a saponification solution, saponifying at 70-90° C. for 3-10 minutes, and drying; 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.

10. The method for forming a high-precision thin-walled steel pipe based on cold rolling and cold drawing coordination according to claim 8, characterized in that: The modified molybdenum disulfide is prepared by dissolving a portion of dopamine in a Tris buffer solution, then adding nano-zirconium phosphate and flaky molybdenum disulfide, uniformly dispersing the mixture by ultrasonication, then adding the remaining dopamine, stirring the mixture at room temperature for 24 hours, centrifuging and washing the mixture, and freeze-drying the mixture to obtain the modified molybdenum disulfide; the mass ratio of dopamine, nano-zirconium phosphate, and flaky molybdenum disulfide is 2:1:1.

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