A metastable austenitic stainless steel for mine fluid delivery pipes and a method for manufacturing the same

Abstract

The application discloses a spinodal austenitic stainless steel for mine fluid conveying pipes and a manufacturing method thereof, and relates to the technical field of stainless steel manufacturing. The spinodal austenitic stainless steel for mine fluid conveying pipes and the manufacturing method thereof are characterized in that a full-process matching manufacturing process is designed according to the material properties of high-manganese low-nickel nitrogen-controlled spinodal austenitic stainless steel. In the smelting stage, step-by-step reduction and argon blowing are adopted to precisely control nitrogen. In the hot rolling stage, a combination of temperature, deformation, descaling, hot coiling, and step final rolling is adopted for pipe control. In addition, the spinodal austenitic stainless steel is matched with graded annealing and two-stage pickling. The hot rolling edge crack defect is eliminated, and the mechanical property difference between the head and tail of the whole coil is greatly reduced. The finished product has high strength, high elongation rate and low hardness, excellent cold forming and welding performance, no oxide skin and color difference defect on the plate surface, and high product qualification rate.

Description

Technical Field

[0001] This application belongs to the field of stainless steel manufacturing technology, and in particular relates to a metastable austenitic stainless steel for mining fluid transport pipes and its manufacturing method. Background Technology

[0002] Mining fluid transport pipelines transport slurries containing solid particles and corrosive media for extended periods, operating under harsh conditions. This necessitates steel with high strength, high plasticity, excellent corrosion resistance, and good formability and weldability. Traditional 304 stainless steel has a high nickel content, leading to significant cost pressures. Meanwhile, ordinary nickel-saving austenitic stainless steels (such as 200 series and 304K2 metastable steels) are prone to edge cracking during hot rolling due to the unique characteristics of their composition (high manganese, low nickel, controlled nitrogen) and microstructure (metastable austenite) when using conventional stainless steel production processes. Furthermore, they are susceptible to defects such as microstructure instability, fluctuating mechanical properties, surface peeling, or over-corrosion during heat treatment and pickling, making it difficult to achieve large-scale, stable, and high-quality production of steel for mining pipelines.

[0003] Existing general processes lack specific matching for this type of special material in terms of heating regime, deformation procedure, temperature control and surface treatment parameters, resulting in low product qualification rate and failure to meet the mining industry's requirements for high reliability and long service life of pipeline materials. Summary of the Invention

[0004] To address some or all of the technical problems existing in the prior art, this application provides a metastable austenitic stainless steel for mining fluid transport pipes and a method for manufacturing the same.

[0005] This application provides a method for manufacturing metastable austenitic stainless steel hot-rolled coils for mining fluid transport pipes, wherein the stainless steel comprises, by mass percentage: C 0.02%–0.08%, Si 0.10%–1.00%, Mn 3.50%–5.50%, P≤0.045%, S≤0.015%, Cr 15.00%–17.00%, Ni 4.50%–6.50%, N 0.020%–0.100%, with the balance being Fe and unavoidable impurities; The manufacturing method includes, in sequence, a steelmaking process, a hot rolling process, and an annealing and pickling process; In the steelmaking process, the AOD refining and reduction stage uses a step-by-step reduction process to control the manganese content, and after the reduction is completed, the argon blowing process is used to precisely adjust the nitrogen content of the liquid steel to the target range. In the hot continuous rolling process, the slab homogenization temperature is controlled at 1200-1250℃; descaling is carried out in multiple passes during the roughing stage, but no descaling is set at the finishing rolling entrance; the number of roughing passes is matched according to the actual width of the slab; the hot coil box is configured according to the thickness and width of the finished product; the final rolling temperature is controlled in a stepped manner according to the thickness of the finished product. In the annealing and pickling process, the target plate temperature for continuous annealing is controlled at 1100-1150℃, and the annealing process speed is set according to the thickness of the strip. The pickling process consists of two steps: hydrochloric acid pretreatment and nitric acid-hydrofluoric acid mixed acid main washing.

[0006] Preferably, the step-by-step reduction process of the steelmaking process is as follows: first, silicon-manganese alloy is added to the molten steel to complete the initial reduction, and then ferrosilicon is added to carry out the deep reduction; the argon blowing process stabilizes the nitrogen content in the steel to the design range by controlling the argon gas flow rate and the blowing time.

[0007] Preferably, the hot rolling process meets the following requirements: High-pressure water is used for descaling in the second and fifth passes of the coarse stage. When the slab width is less than 1580mm, 5 passes of rough rolling are configured; when the slab width is greater than or equal to 1580mm, 7 passes of rough rolling are configured. When the finished product thickness is less than 5.0 mm, it should be placed in the hot rolling box; when the finished product thickness is between 5.0 mm and 6.0 mm and the finished product width is greater than 1500 mm, it should be placed in the hot rolling box; other combinations of thickness and width should not be placed in the hot rolling box. When the finished product thickness is <2.5mm, the final rolling temperature is controlled at 960~1000℃; when the finished product thickness is ≥2.5mm, the final rolling temperature is controlled at 1000~1040℃.

[0008] Preferably, the annealing and pickling process meets the following requirements: The annealing process adopts a graded control of TV value, where TV is the product of strip thickness and unit operating line speed; when the strip thickness is ≤3.0mm, TV is controlled at 150~180; when the strip thickness is 3.0mm<h≤6.0mm, TV is controlled at 160~190. The concentration of hydrochloric acid in the pretreatment section is 160–200 g / L, and the temperature of the acid solution is controlled at 50–70 °C. In the main washing section where nitric acid and hydrofluoric acid are mixed, the concentration of nitric acid is 140-180 g / L and the concentration of hydrofluoric acid is 25-30 g / L. The temperature of the mixed acid solution is controlled at 40-60℃.

[0009] This application provides a metastable austenitic stainless steel hot-rolled coil for mining fluid transport pipes, which is manufactured by the above-mentioned manufacturing method.

[0010] The metastable austenitic stainless steel for mining fluid transport pipes and its manufacturing method disclosed in this application have the following advantages and positive effects: A complete manufacturing process was designed to address the material characteristics of high-manganese, low-nickel, nitrogen-controlled metastable austenitic stainless steel. This process involves step-by-step reduction and precise nitrogen control via argon blowing during the smelting stage, combined with temperature control, deformation management, descaling, hot rolling box operation, and stepped final rolling during the hot rolling stage. This, along with graded annealing and two-stage pickling, eliminates edge crack defects during hot rolling and significantly reduces the difference in mechanical properties between the beginning and end of the coil. The finished product exhibits high strength, high elongation, and low hardness, with excellent cold forming and welding performance. Furthermore, the surface of the plate is clean and free of oxide scale and color defects, resulting in a high product qualification rate. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0012] The present application discloses a method for manufacturing metastable austenitic stainless steel hot-rolled coils for use in mining fluid transport pipes. The stainless steel comprises, by mass percentage: C 0.02%–0.08%, Si 0.10%–1.00%, Mn 3.50%–5.50%, P≤0.045%, S≤0.015%, Cr 15.00%–17.00%, Ni 4.50%–6.50%, N 0.020%–0.100%, with the balance being Fe and unavoidable impurities.

[0013] The manufacturing process includes, in sequence, steelmaking, hot rolling, and annealing and pickling. Steelmaking process: The steelmaking process involves electric arc furnace primary refining, AOD refining, LF refining, and continuous casting to prepare qualified slabs.

[0014] In the AOD refining and reduction stage, a step-by-step reduction process is used to control the manganese content. After the reduction is completed, an argon blowing process is used to precisely adjust the nitrogen content of the liquid steel to the target range.

[0015] Specifically, the step-by-step reduction process in steelmaking is as follows: First, silicon-manganese alloy is added to the molten steel to complete the initial reduction, initially controlling the manganese content and completing the main deoxidation reduction. Then, ferrosilicon is added to carry out deep reduction, further reducing the oxygen content of the molten steel and stabilizing the manganese yield. The argon blowing process stabilizes the nitrogen content in the steel to the design range by controlling the argon gas flow rate and duration, and in conjunction with the composition system, ensures the stability of the metastable austenitic structure.

[0016] Hot rolling process: The hot continuous rolling process sequentially heats, roughs, finishes, and coils the ground slab, with process parameters matched and controlled throughout the process to suit the microstructure characteristics of metastable austenitic stainless steel.

[0017] During the slab heating stage, the slab homogenization temperature is controlled at 1200-1250℃. This ensures that the alloying elements are fully dissolved, prevents abnormal growth of austenite grains, maintains the high-temperature plasticity range of the steel grade, and reduces the risk of edge cracking during rolling.

[0018] In the descaling process, a differentiated setup is adopted, with multiple descaling passes in the roughing stage and no descaling at the finish rolling entrance. High-pressure water descaling is applied in the second and fifth passes of the roughing stage to remove the initial thick iron oxide scale on the slab surface. The descaling process is omitted at the finish rolling entrance, which reduces the temperature drop of the strip and avoids the formation of a dense chromium-rich oxide layer that is difficult to remove by pickling due to secondary oxidation on the surface.

[0019] The number of roughing passes is matched to the actual width of the slab: 5 passes are configured when the slab width is <1580mm, and 7 passes are configured when the slab width is ≥1580mm. Under the same total deformation, increasing the number of rolling passes for wide slabs can distribute the total reduction, reduce the deformation per pass, and reduce the tensile stress on the slab edges during rolling, thereby reducing the tendency for edge cracks to form from the perspective of deformation control.

[0020] The hot-rolling box is used based on the thickness and width of the finished product. Finished products with a thickness < 5.0 mm are placed in the hot-rolling box; finished products with a thickness of 5.0 mm to 6.0 mm and a width > 1500 mm are also placed in the hot-rolling box; other thickness and width combinations are not placed in the hot-rolling box. The hot-rolling box's heat preservation and temperature equalization function helps to balance the temperature of the strip's beginning and end, reducing the difference in microstructure and mechanical properties between the two ends.

[0021] The final rolling temperature is controlled in a stepped manner according to the thickness of the finished product. When the finished product thickness is <2.5mm, the final rolling temperature is controlled at 960~1000℃; when the finished product thickness is ≥2.5mm, the final rolling temperature is controlled at 1000~1040℃. This ensures that the microstructure of strip steel of different thicknesses is uniform after rolling.

[0022] Annealing and pickling process: The annealing and pickling process is completed in a continuous annealing and pickling unit. The target plate temperature for continuous annealing is controlled at 1100-1150℃, and the annealing process speed is set according to the thickness of the strip. The pickling process consists of two steps: hydrochloric acid pretreatment and nitric acid-hydrofluoric acid mixed acid main washing.

[0023] The annealing and pickling process must meet the following requirements: The annealing process employs a tiered control system based on the TV value, where TV is the product of the strip thickness and the furnace operating speed. For strip thicknesses ≤ 3.0 mm, TV is controlled between 150 and 180; for strip thicknesses between 3.0 mm and h ≤ 6.0 mm, TV is controlled between 160 and 190. By matching the strip thickness with the furnace operating speed, sufficient and uniform holding time is ensured for strips of different specifications within the furnace, achieving adequate recrystallization and alloy solution treatment.

[0024] In the pickling process, the hydrochloric acid pretreatment section has an acid concentration of 160–200 g / L and an acid temperature controlled at 50–70°C, used to peel off the loose iron oxide scale on the surface of the strip steel. In the nitric acid-hydrofluoric acid mixed main washing section, the nitric acid concentration is 140–180 g / L and the hydrofluoric acid concentration is 25–30 g / L, with the mixed acid temperature controlled at 40–60°C. Strict control of the concentration, temperature, and iron ion content of each tank solution is maintained, used to dissolve the dense, chromium-rich inner oxide layer. The combined pickling of these two stages thoroughly removes the surface oxide scale while preventing over-corrosion and surface color differences in the strip steel.

[0025] To illustrate the technical effects of this application more specifically, the following examples and comparative examples are provided for comparison.

[0026] All examples and comparative examples are based on the same target chemical composition (mass percentage, wt.%): C: 0.05%, Si: 0.60%, Mn: 4.80%, P: 0.030%, S: 0.002%, Cr: 16.20%, Ni: 5.30%, N: 0.08%.

[0027] Example 1 (Production of metastable austenitic stainless steel hot-rolled coil with a thickness of 2.0 mm and a width of 1250 mm) Steelmaking process: The entire process of electric arc furnace primary refining, AOD step-by-step reduction for manganese control, argon blowing for precise nitrogen adjustment, LF refining and fine adjustment, continuous casting and slab grinding is adopted to ensure that the composition of the molten steel is uniform and the nitrogen content is stable within the target range.

[0028] Hot rolling process: The slab after grinding is sent to the heating furnace for segmented heating. The temperature of the soaking section is stably controlled at 1240℃ and held until the temperature inside and outside the slab is uniform. After exiting the furnace, the slab is sent to the roughing mill for rolling. Since the slab width is 1250mm < 1580mm, 5 passes of roughing are configured. The roughing mill exit temperature (RDT) is controlled at 1100℃. High-pressure water descaling is carried out in the second and fifth passes of the roughing stage. No descaling process is set at the entrance of the finishing mill. The finished product thickness is 2.0mm < 5.0mm. The intermediate slab of the roughing mill is coiled and kept warm in a hot coil box. Then the intermediate slab is sent to the finishing mill to complete the final rolling. The finished product thickness is < 2.5mm. The final rolling temperature is controlled at 1000℃. After rolling, the hot-rolled steel coil is obtained.

[0029] Annealing and pickling process: After the hot-rolled steel coil is uncoiled, it is sent to the continuous annealing and pickling unit. The target plate temperature of the continuous annealing furnace is controlled at 1130℃. The strip thickness is 2.0mm≤3.0mm. The annealing process is controlled according to TV=165 and matched with the corresponding unit operating speed. Pickling is carried out according to the set parameters to complete hydrochloric acid pretreatment and mixed acid main washing to ensure surface quality.

[0030] Test results Finished product tensile strength R m =655MPa, specified plastic elongation strength R p0.2 =285MPa, elongation after fracture A=38%, Vickers hardness HV=195; the steel plate is straight, the edges are intact without cracks, the surface is uniformly silvery white, and there are no oxide scale residues, over-corrosion and color difference defects.

[0031] Example 2 (Production of metastable austenitic stainless steel hot-rolled coil with a thickness of 4.5 mm and a width of 1650 mm) Steelmaking process: The entire process of electric arc furnace primary refining, AOD step-by-step reduction for manganese control, argon blowing for precise nitrogen adjustment, LF refining and fine adjustment, continuous casting and slab grinding is adopted to ensure that the composition of the molten steel is uniform and the nitrogen content is stable within the target range.

[0032] Hot rolling process: The slab heating and homogenization temperature is controlled at 1240℃, and it is kept at this temperature until the internal and external temperatures are uniform before exiting the furnace; the slab width is 1650mm ≥ 1580mm, and a 7-pass roughing rolling process is configured, with the roughing mill exit temperature (RDT) controlled at 1090℃; the second and fifth passes of the roughing mill are subjected to high-pressure water descaling, while no descaling process is set at the entry of the finishing mill; the finished product thickness is 4.5mm < 5.0mm, and it is put into a hot coil box for heat preservation and homogenization; the finished product thickness is ≥ 2.5mm, and the final rolling temperature is controlled at 1000℃, and it is coiled after rolling.

[0033] Annealing and pickling process: The target plate temperature of the continuous annealing furnace is controlled at 1130℃; the strip thickness is 4.5mm and falls within the range of 3.0mm<h≤6.0mm. The annealing process is controlled according to TV=185 and matched with the corresponding unit operating speed; the pickling process completes hydrochloric acid pretreatment and mixed acid main washing according to the set parameters to ensure surface quality.

[0034] Test results Finished product tensile strength R m =635MPa, specified plastic elongation strength R p0.2 =270MPa, elongation after fracture A=32%, Vickers hardness HV=205; hot-rolled edge without cracks, good plate shape, excellent surface quality after pickling, no obvious defects.

[0035] Example 3 (Production of metastable austenitic stainless steel hot-rolled coil with a thickness of 6.5 mm and a width of 1800 mm) Steelmaking process: The entire process of electric arc furnace primary refining, AOD step-by-step reduction for manganese control, argon blowing for precise nitrogen adjustment, LF refining and fine adjustment, continuous casting and slab grinding is adopted to ensure that the composition of the molten steel is uniform and the nitrogen content is stable within the target range.

[0036] Hot rolling process: The slab heating and homogenization temperature is controlled at 1240℃, and it is kept at a uniform temperature before being removed from the furnace; the slab width is 1800mm≥1580mm, and a 7-pass roughing rolling is configured, with the roughing mill exit temperature (RDT) controlled at 1090℃; high-pressure water descaling is used in the second and fifth passes of the roughing mill, and no descaling process is set at the entrance of the finishing mill; for finished product thickness of 6.5mm, which is in the range of 6.0~8.0mm and finished product width of 1800mm>>1500mm, a hot coil box is used to balance the head and tail temperature difference of the thick and wide strip steel; for finished product thickness ≥2.5mm, the final rolling temperature is controlled at 1000℃, and the strip is coiled after rolling.

[0037] Annealing and pickling process: The target plate temperature of the continuous annealing furnace is raised to 1150℃ to ensure that the alloy elements of the thick strip steel are fully dissolved; the strip steel thickness corresponds to the 3.0mm<h≤6.0mm range, and TV=185 is used for control to match the corresponding unit operating speed; the pickling is carried out according to the set parameters to complete the hydrochloric acid pretreatment and mixed acid main wash to ensure surface quality.

[0038] Test results Finished product tensile strength R m =625MPa, specified plastic elongation strength R p0.2 =265MPa, elongation after fracture A=28%, Vickers hardness HV=210; the steel plate has uniform microstructure and properties along its entire length, good edge quality, and a clean surface free of oxide scale residue and color difference defects.

[0039] Comparative Example 1 (Metastable austenitic hot-rolled coil with a thickness of 3.0 mm and a width of 1500 mm produced using conventional 304 stainless steel processes) Steelmaking process: Conventional 304 stainless steel smelting process is adopted. Qualified slabs are prepared through electric arc furnace primary refining, AOD refining, LF refining, and continuous casting.

[0040] Hot rolling process: The slab heating and homogenization temperature is increased to 1260℃, and a conventional stainless steel heating system is adopted; the roughing rolling is configured according to the general pass configuration, and the descaling process is retained at the entrance of the finishing rolling; the hot coil box is not used throughout the process; the final rolling temperature is uniformly controlled at 1050℃, and is not graded and controlled according to thickness.

[0041] Annealing and pickling process: General annealing and pickling parameters for 304 stainless steel are adopted. The target plate temperature of the continuous annealing furnace is 1080℃, and the process speed is constant at 100m / min. It is not graded and matched according to the thickness of the strip steel. The pickling solution adopts the conventional production ratio of 304 and no specific adjustments are made.

[0042] Test results Obvious microcracks appeared at the edge of the hot-rolled coil, with a crack length of approximately 50-200 mm and a depth of approximately 0.5-1.0 mm; the mechanical properties of the finished product fluctuated greatly, and the tensile strength R... m The surface hardness fluctuates between 600 and 650 MPa, and the elongation after fracture (A) fluctuates between 18% and 25%. The Vickers hardness reaches as high as 235 HV in some local areas. After pickling, there are local color differences and slight oxide scale residue on the surface, and the defect rate increases significantly.

[0043] Comparative Analysis of Effects Compared with the conventional process used in Comparative Example 1, the metastable stainless steel hot-rolled coils obtained in the three embodiments of this application can effectively avoid hot-rolling edge cracking defects, significantly improve the uniformity of the mechanical properties of the finished product, especially the elongation after fracture, and have lower overall hardness with stable range. Simultaneously, the surface quality of the steel plate is superior, resulting in a significant improvement in overall product performance. This fully demonstrates that the complete set of targeted production processes provided in this application has irreplaceable creativity and outstanding technical effects in solving the specific technical challenges of manufacturing hot-rolled coils of metastable austenitic stainless steel for mining fluid transport pipes.

[0044] This application designs a complete manufacturing process for high-manganese, low-nickel, nitrogen-controlled metastable austenitic stainless steel, which addresses the material characteristics of the product. Through step-by-step reduction and precise nitrogen control via argon blowing during the smelting stage, and combined control of temperature, deformation, descaling, hot rolling box, and stepped final rolling during the hot rolling stage, along with graded annealing and two-stage pickling, the process eliminates edge crack defects during hot rolling and significantly reduces the difference in mechanical properties between the beginning and end of the coil. The finished product combines high strength, high elongation, and low hardness, exhibiting excellent cold forming and welding performance. Furthermore, the plate surface is clean and free of oxide scale and color difference defects, and the product qualification rate is high.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for manufacturing metastable austenitic stainless steel hot-rolled coils for mining fluid transport pipes, characterized in that, The stainless steel comprises, by mass percentage: C 0.02%–0.08%, Si 0.10%–1.00%, Mn 3.50%–5.50%, P≤0.045%, S≤0.015%, Cr 15.00%–17.00%, Ni 4.50%–6.50%, N 0.020%–0.100%, with the balance being Fe and unavoidable impurities; The manufacturing method includes, in sequence, a steelmaking process, a hot rolling process, and an annealing and pickling process; In the steelmaking process, the AOD refining and reduction stage uses a step-by-step reduction process to control the manganese content, and after the reduction is completed, the argon blowing process is used to precisely adjust the nitrogen content of the liquid steel to the target range. In the hot continuous rolling process, the slab homogenization temperature is controlled at 1200-1250℃; descaling is carried out in multiple passes during the roughing stage, but no descaling is set at the finishing rolling entrance; the number of roughing passes is matched according to the actual width of the slab; the hot coil box is configured according to the thickness and width of the finished product; the final rolling temperature is controlled in a stepped manner according to the thickness of the finished product. In the annealing and pickling process, the target plate temperature for continuous annealing is controlled at 1100-1150℃, and the annealing process speed is set according to the thickness of the strip. The pickling process consists of two steps: hydrochloric acid pretreatment and nitric acid-hydrofluoric acid mixed acid main washing.

2. The method for manufacturing metastable austenitic stainless steel hot-rolled coils for mine fluid transport pipes according to claim 1, characterized in that, The step-by-step reduction process of the steelmaking process is as follows: first, silicon-manganese alloy is added to the molten steel to complete the initial reduction, and then ferrosilicon is added to carry out the deep reduction. Argon blowing process stabilizes the nitrogen content in steel to the design range by controlling the argon gas flow rate and duration.

3. The method for manufacturing metastable austenitic stainless steel hot-rolled coils for mine fluid transport pipes according to claim 1, characterized in that, The hot rolling process meets the following requirements: High-pressure water is used for descaling in the second and fifth passes of the coarse stage. When the slab width is less than 1580mm, 5 passes of rough rolling are configured; when the slab width is greater than or equal to 1580mm, 7 passes of rough rolling are configured. When the finished product thickness is less than 5.0 mm, it should be placed in the hot rolling box; when the finished product thickness is between 5.0 mm and 6.0 mm and the finished product width is greater than 1500 mm, it should be placed in the hot rolling box; other combinations of thickness and width should not be placed in the hot rolling box. When the finished product thickness is <2.5mm, the final rolling temperature is controlled at 960~1000℃; when the finished product thickness is ≥2.5mm, the final rolling temperature is controlled at 1000~1040℃.

4. The method for manufacturing metastable austenitic stainless steel hot-rolled coils for mine fluid transport pipes according to claim 1, characterized in that, The annealing and pickling process meets the following requirements: The annealing process adopts TV value graded control; when the strip thickness is ≤3.0mm, TV is controlled at 150~180; when the strip thickness is 3.0mm<h≤6.0mm, TV is controlled at 160~190. The concentration of hydrochloric acid in the pretreatment section is 160–200 g / L, and the temperature of the acid solution is controlled at 50–70 °C. In the main washing section where nitric acid and hydrofluoric acid are mixed, the concentration of nitric acid is 140-180 g / L and the concentration of hydrofluoric acid is 25-30 g / L. The temperature of the mixed acid solution is controlled at 40-60℃.

5. A metastable austenitic stainless steel hot-rolled coil for use in mining fluid transport pipes, characterized in that... It is produced by the manufacturing method described in any one of claims 1 to 4.