A steel for fire extinguisher cylinder, its preparation method and application

Abstract

This invention discloses a steel for fire extinguisher cylinders, its preparation method, and its application, relating to the field of iron and steel smelting technology. By controlling the elemental composition of the continuously cast billet, particularly the carbon and manganese content, not only can the steel maintain high strength under high-temperature conditions, but the high-temperature rotational undercut in the preparation of fire extinguisher cylinders is also eliminated. Simultaneously, while ensuring the steel's strength, it also provides good weldability and formability. By controlling the temperature parameters of the annealing process, combined with the elemental content in the continuously cast billet, the microstructure of the prepared steel can be controlled. Holding at the soaking temperature provided by this invention allows carbon dissolution in the steel to reach equilibrium, preventing excessive grain growth that could affect the steel's strength. Furthermore, by controlling the temperature of the over-aging stage, the distribution of carbides and the content of dissolved carbon are controlled, improving the steel's strength while preventing the fire extinguisher cylinders made from this steel from aging and becoming unusable during subsequent use.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting technology, and more specifically, to a steel for fire extinguisher cylinders, its preparation method, and its application. Background Technology

[0002] Because the cylinder of a fire extinguisher is typically manufactured by rolling steel strips or plates into a circular shape, welding them together while rolling, and then high-temperature spinning to close the end, the steel strips or plates must possess certain formability and good weldability. Furthermore, due to this manufacturing process, the steel strips or plates used in its production need to have sufficient strength to ensure high strength during the high-temperature spinning process and prevent dents. Simultaneously, the fire extinguisher contains extinguishing media, which is generally under high pressure. During use, the fire extinguisher is exposed to a high-temperature environment due to the fire, requiring the fire extinguisher to remain undeformed or leak during both storage and use.

[0003] Currently, the strength and elongation of the steel used to manufacture fire extinguishers cannot simultaneously meet their manufacturing requirements. Therefore, there is an urgent need to propose a steel that meets the requirements for manufacturing fire extinguisher cylinders in order to meet market demand.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a steel for fire extinguisher cylinders, its preparation method, and its application.

[0006] This invention is implemented as follows:

[0007] In a first aspect, the present invention provides a method for preparing steel for fire extinguisher cylinders, comprising hot rolling, pickling and cold rolling followed by annealing of a continuously cast billet.

[0008] The elemental composition of the continuously cast billet includes C: 0.040-0.08%, Mn: 0.15-0.25%, S: ≤0.015%, P: ≤0.025%, Si: ≤0.030%, Al: 0.030-0.060%, N: ≤0.0050%, with the remainder being Fe and other unavoidable impurities.

[0009] The soaking temperature of the annealing process is 760–800℃, and the over-aging temperature is 360–400℃.

[0010] Secondly, the present invention provides a steel for fire extinguisher cylinders, which is prepared by the preparation method provided in any of the foregoing embodiments, and the metallographic structure of the steel includes ferrite and cementite.

[0011] Thirdly, the present invention provides a preparation method as provided in any of the foregoing embodiments or the application of fire extinguisher cylinder steel as provided in any of the foregoing embodiments in the preparation of fire-fighting steel tools.

[0012] The present invention has the following beneficial effects:

[0013] This invention provides a steel for fire extinguisher cylinders, its preparation method, and its application. By controlling the elemental composition of the continuously cast billet, particularly the carbon and manganese content, the steel not only maintains high strength under high-temperature conditions but also eliminates high-temperature rotational undercut during fire extinguisher cylinder preparation. Furthermore, it ensures good weldability and formability while maintaining the steel's strength. By controlling the temperature parameters of the annealing process and the elemental content in the continuously cast billet, the microstructure of the prepared steel can be controlled. Holding the steel at the soaking temperature provided by this invention allows carbon dissolution to reach equilibrium, resulting in limited grain growth and preventing excessive grain growth that could negatively impact the steel's strength. Finally, by controlling the temperature of the over-aging stage, the distribution of carbides and the content of dissolved carbon are controlled, improving the steel's strength while preventing aging and product scrapping of fire extinguisher cylinders made from this steel during subsequent use. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 A scanning electron microscope image of the steel used for the fire extinguisher cylinder provided in Embodiment 1 of the present invention;

[0016] Figure 2 This is a scanning electron microscope image of the steel used for the fire extinguisher cylinder provided in Embodiment 4 of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0018] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0019] In a first aspect, the present invention provides a method for preparing steel for fire extinguisher cylinders, comprising hot rolling, pickling and cold rolling followed by annealing of a continuously cast billet.

[0020] The elemental composition of the continuously cast billet includes C: 0.040-0.08%, Mn: 0.15-0.25%, S: ≤0.015%, P: ≤0.025%, Si: ≤0.030%, Al: 0.030-0.060%, N: ≤0.0050%, with the remainder being Fe and other unavoidable impurities.

[0021] Preferably, the elemental composition of the continuously cast billet includes C: 0.045-0.065%, Mn: 0.15-0.20%, S: ≤0.010%, P: ≤0.015%, Si: ≤0.025%, Al: 0.030-0.045%, N: ≤0.0040%, with the remainder being Fe and other unavoidable impurities.

[0022] The soaking temperature of the annealing process is 760–800℃, and the over-aging temperature is 360–400℃.

[0023] The reason why the elemental composition of the steel used for the fire extinguisher cylinder provided by this invention is controlled within the above-mentioned range is:

[0024] C: A strengthening element for steel. To control the strength of steel, its content is controlled between 0.04% and 0.08%.

[0025] Si: Degrades the surface properties of steel. As the Si content increases, the iron oxide scale on the steel becomes difficult to remove, affecting the effectiveness of the pickling process. Therefore, the silicon content must be controlled within a low range.

[0026] Mn: Appropriate amounts of Mn are used to supplement the strength of steel. At the same time, Mn can also play a deoxidizing role, reducing the oxygen content in the product and thus improving the product's processability. Mn can also combine with S to form high-melting-point MnS, reducing the content of low-melting-point FeS and preventing the product from becoming hot brittle.

[0027] P: P is a harmful element in steel. Although it increases the strength of the material, it also increases the cold brittleness of the steel and reduces the plasticity of the material. Generally, the lower the better. In order to ensure the excellent performance of the product, the P content is controlled at ≤0.025%.

[0028] S: S is a harmful element in steel, which can form inclusions and reduce the ductility and toughness of steel. Generally, the lower the better. In order to ensure the excellent performance of the product, the S content is controlled to be ≤0.015%.

[0029] Al: Al is a strong deoxidizer and has a strong binding force with N. The AlN generated during the reaction process can reduce the aging of the finished product, and AlN can inhibit grain growth in steel. By controlling its proportion within the range of this invention, it can refine the grains during steel heating and annealing.

[0030] N: A strengthening element for steel. A small amount of N can be added to increase the strength of steel.

[0031] By controlling the elemental composition of the continuously cast billet within the aforementioned range and combining this with temperature control during the annealing process, the rolled piece is held at a temperature of 760–800°C in the soaking zone. This allows the carbon dissolution in the steel to reach equilibrium, resulting in limited grain growth and preventing excessive grain growth that could affect strength. However, the high cooling rate in the continuous annealing unit hinders the precipitation of solid solution, causing deviations in carbide precipitation during the cooling stage. Only by adjusting the temperature of the over-aging zone can the distribution of carbides and the content of dissolved carbon be controlled, thereby obtaining the desired ratio of ferrite and cementite to eliminate the effects of aging. This invention controls the over-aging temperature within 360–400°C, allowing dissolved carbon in the steel to precipitate and form 5–10% cementite. This improves the strength of the steel while preventing the fire extinguisher cylinders made from this steel from aging and becoming unusable during subsequent use.

[0032] In an optional implementation, annealing includes a preheating section, a heating section, a soaking section, a slow cooling section, a rapid cooling section, an over-aging section, and a final cooling section.

[0033] The preheating section, heating section, soaking section, and slow cooling section constitute the first stage of annealing. Their main function is to recrystallize the ferrite in the steel and to grow the ferrite grains. However, as described above, due to the control of the temperature of the soaking section in this invention, the grain growth in the first stage will not be unlimited, but rather limited and controllable, thus ensuring the strength of the steel while avoiding brittle fracture.

[0034] The rapid cooling section, the over-aging section, and the final cooling section are the second stage of annealing. Their main function is to determine the distribution of cementite in the microstructure and the content of supersaturated solid solution carbon, ensuring that the quality of the steel meets the manufacturing requirements of fire extinguisher cylinders.

[0035] Preferably, the preheating zone temperature is 130–140°C, the heating zone temperature is 750–800°C, the soaking zone temperature is 760–800°C, the slow cooling zone temperature is 640–660°C, the rapid cooling zone temperature is 390–410°C, the over-aging zone temperature is 360–400°C, and the final cooling zone temperature is 170–190°C.

[0036] Preferably, the preheating section temperature is 130–135°C, the heating section temperature is 780–795°C, the soaking section temperature is 780–790°C, the slow cooling section temperature is 640–650°C, the rapid cooling section temperature is 400–410°C, the over-aging section temperature is 380–390°C, and the final cooling section temperature is 175–190°C.

[0037] In an optional implementation, annealing is performed using a vertical continuous annealing furnace.

[0038] In an optional embodiment, hot rolling includes rough rolling, wherein the thickness of the intermediate billet obtained by rough rolling is 15 to 20% of the thickness of the continuously cast billet, preferably 16.5 to 18.5%. For example, when the thickness of the continuously cast billet is 230 mm, the thickness of the intermediate billet obtained by rough rolling is 34.5 to 46 mm, more preferably 38 to 42 mm.

[0039] Preferably, the horizontal rolling mill for roughing includes a first horizontal rolling mill and a second horizontal rolling mill, wherein the first horizontal rolling mill has 3 rolling passes and the second horizontal rolling mill has 3 or 5 rolling passes.

[0040] It is understandable that the roughing process of hot rolling generally consists of a horizontal rolling mill and a vertical rolling mill. The horizontal rolling mill is used to adjust the thickness of the rolled piece, and the vertical rolling mill is used to adjust the width of the rolled piece. There are usually two horizontal and two vertical rolling mills, which are set up alternately. During rolling, the rolled piece passes through the first vertical rolling mill, the first horizontal rolling mill, the second vertical rolling mill, and the second horizontal rolling mill in sequence, and then returns in reverse along the above path for multiple rolling passes to ensure that the intermediate billet obtained after roughing meets the required specifications.

[0041] Preferably, in order to control the shape and thickness accuracy of the intermediate billet, the reduction rate of each roughing pass decreases sequentially. The reduction parameters of the first horizontal rolling mill include: 20-24% reduction rate for the first pass, 18-22% reduction rate for the second pass, and 15-18% reduction rate for the third pass.

[0042] Preferably, the exit temperature of the rolled piece from the first horizontal rolling mill is 1000–1060°C.

[0043] Preferably, in order to improve the surface quality of the rolled piece, descaling operations are included both when the rolled piece enters and leaves the first horizontal rolling mill. Specifically, the descaling operation in roughing can be performed using high-pressure water descaling.

[0044] Preferably, in order to control the shape and thickness accuracy of the intermediate billet, the reduction rate of each roughing pass decreases sequentially. The reduction parameters when the second horizontal rolling mill has 3 rolling passes include: 29-35% reduction rate for the first pass, 32-38% reduction rate for the second pass, and 16-20% reduction rate for the third pass.

[0045] Preferably, in order to control the shape and thickness accuracy of the intermediate billet, the reduction rate of each roughing pass decreases sequentially. The reduction parameters when the second horizontal rolling mill has 5 rolling passes include: 20-24% reduction rate for the first pass, 20-25% reduction rate for the second pass, 20-25% reduction rate for the third pass, 20-24% reduction rate for the fourth pass, and 10-15% reduction rate for the fifth pass.

[0046] Preferably, the reduction parameters for the second horizontal rolling mill when the rolling passes are 5 include: 20-23% reduction for the first pass, 22-25% reduction for the second pass, 21-24% reduction for the third pass, 21-23% reduction for the fourth pass, and 12-15% reduction for the fifth pass.

[0047] Preferably, in order to ensure that the thickness of the intermediate billet is within the aforementioned range, when the width of the continuously cast billet is large or the width reduction is large, it is necessary to increase the number of rolling passes. In some embodiments of the present invention, the above problem is solved by increasing the number of rolling passes of the second horizontal roll. Specifically, when the rolling width of the rolled piece is >1300mm and / or the width reduction of the rolled piece is >50mm, the number of rolling passes of the second horizontal roll mill is 5.

[0048] Preferably, the exit temperature of the rolled piece in the second horizontal rolling mill is 970–1030°C.

[0049] Preferably, in order to ensure the rolling temperature and final rolling temperature of the second horizontal rolling mill, the workpiece is descaled only before entering the second horizontal rolling mill.

[0050] Because the steel used for fire extinguisher cylinders has high strength, a 3+3 or 3+5 rolling pattern is adopted for rough rolling. This means the first horizontal roll is rolled in 3 passes, and the second horizontal roll is rolled in 3 or 5 passes. This ensures that the resulting steel has higher strength. The rough rolling parameters are controlled within the above range because the workpiece temperature is high during rough rolling, resulting in low deformation resistance, good plasticity, and a larger total reduction rate in the rough rolling mill, thus reducing the load on the finishing mill.

[0051] In an optional implementation, since roughing is a hot rolling process, the continuous casting billet needs to be heated before roughing to ensure effective deformation of the continuous casting billet into the rolled product. Heating is carried out in a heating furnace with a heating temperature of 1200-1240°C.

[0052] In an optional embodiment, hot rolling further includes finish rolling, which involves rolling the intermediate billet obtained from rough rolling. The final rolling temperature of the rolled piece during finish rolling is 860–900°C, preferably 870–890°C. Controlling the final rolling temperature within the above range allows for more complete recrystallization of ferrite, enabling the ferrite grains to grow to a suitable grain size.

[0053] Preferably, after finishing rolling, the rolled piece is further subjected to laminar flow cooling, which is front-stage cooling. The opening degree of the upper and lower manifolds for front-stage cooling is 70-80%, more preferably 75%. Controlling the opening degree of the upper and lower manifolds for cold flow cooling within the above range can effectively refine the grains.

[0054] Preferably, after laminar cooling, the rolled piece is coiled to obtain a hot-rolled coil. In order to meet the high strength requirements of the steel used for fire extinguisher cylinders, it is necessary to control the grain growth during the coiling process to prevent the grain growth from affecting the steel's performance due to excessively high coiling temperature. Therefore, the coiling temperature is 600-660℃, preferably 620-660℃.

[0055] In an optional embodiment, pickling cold rolling includes pickling the hot-rolled piece and then placing it in a pickling and rolling unit for rolling.

[0056] Preferably, the parameters of the pickling and cold rolling process include: pickling temperature 75-85℃, stretch leveler elongation 1.5-2.5%, cold rolling reduction 70-80%, roughness of the pickling and rolling S5 stand rolls 3.5-4.5μm, and unit rolling force of the pickling and rolling S5 stand rolls 5-7MN / m.

[0057] In an optional embodiment, the annealed rolled piece is further subjected to leveling and tension straightening, wherein the surface roughness of the leveling work roll is 3-4 μm, the elongation of the leveling is 0.6-1.3%, and the elongation of the tension straightening is 0.03-0.1%.

[0058] In an optional embodiment, the preparation of the continuously cast billet sequentially includes hot metal desulfurization, converter smelting, argon blowing of the smelted steel, refining through an RH furnace, and then continuous casting of the steel into a continuously cast billet. The above preparation process yields purer steel, eliminates surface inclusions and sand holes, and can be performed using existing smelting methods, as long as the elemental composition of the continuously cast billet is within the range described in this invention.

[0059] In some embodiments, the method for preparing steel for fire extinguisher cylinders provided by the present invention includes the following steps in sequence: desulfurization of molten iron; converter smelting; argon blowing of the molten steel smelted in the converter; RH furnace refining; continuous casting of the refined molten steel into a continuous casting billet; hot rolling of the continuous casting billet (including rough rolling and finish rolling, after which laminar cooling is performed and the billet is coiled to obtain a hot-rolled coil); pickling of the hot-rolled coil; cold continuous rolling of the pickled coil; leveling and tensioning to obtain steel for fire extinguisher cylinders.

[0060] In an optional embodiment, the steel used for the fire extinguisher cylinder produced by any of the above methods of the present invention is steel strip or steel plate.

[0061] Secondly, the present invention provides a steel for fire extinguisher cylinders, which is prepared by the preparation method provided in any of the foregoing embodiments, and the metallographic structure of the steel includes ferrite and cementite.

[0062] In an optional embodiment, the metallographic structure of the steel is ferrite and cementite, with the ferrite content being 90-95%, the cementite content being 5-10%, and the ferrite grain size being 8.0-8.5.

[0063] Because fire extinguishers are placed under high pressure, they require high strength. Simultaneously, due to processing requirements, the substrate needs a certain degree of plasticity. This invention controls the strength and plasticity of the steel primarily through composition control and annealing temperature to obtain a suitable metallographic structure. In terms of composition, carbon (C) and fe (Fe) form cementite, which strengthens the steel; part of manganese (Mn) eliminates the harmful effects of sulfur (S), while the remainder is dissolved in ferrite, providing solid solution strengthening. The soaking temperature of the annealing process is controlled at 760–800℃, which controls the ferrite grain size to 8.0–8.5, resulting in finer grains. The over-aging temperature is controlled at 360–400℃, causing carbon (C) in the ferrite to precipitate, forming cementite, which provides precipitation strengthening and prevents aging during subsequent use. The metallographic structure of the fire extinguisher cylinder steel obtained after controlling the above parameters is ferrite and a small amount of cementite, with ferrite accounting for 90–95% and cementite content for 5–10%.

[0064] Preferably, the steel has a yield strength of 210–280 MPa, a tensile strength of 320–410 MPa, and an elongation of A. 80 With a content of ≥35% and a surface roughness Ra of 0.70~1.60μm, it fully meets the requirements for steel used in fire extinguisher cylinders. Furthermore, the steel has good formability and weldability, and no dents are produced under high-temperature spinning. Therefore, there are no problems with leakage or cracking after the fire extinguisher cylinder is made.

[0065] Thirdly, the present invention provides a preparation method as provided in any of the foregoing embodiments or the application of fire extinguisher cylinder steel as provided in any of the foregoing embodiments in the preparation of fire-fighting steel tools.

[0066] Example 1

[0067] This embodiment provides a method for preparing steel for fire extinguisher cylinders, including the following steps:

[0068] S01. Preparation of continuous casting billet

[0069] The existing smelting method involves sequential desulfurization of molten iron, converter smelting, argon blowing of the molten steel, refining in an RH furnace, and then continuous casting into a continuously cast billet. The composition of the continuously cast billet is: C: 0.062%, Mn: 0.15%, S: 0.006%, P: 0.013%, Si: 0.021%, Alt: 0.032%, N: 0.0032%, with the remainder being Fe and other unavoidable impurities: 99.7128%.

[0070] S02, hot rolled

[0071] S021. Heating: Place the continuously cast billet in a heating furnace and heat it to 1213℃.

[0072] S022, Rough Rolling: The heated continuously cast billet is placed in a rough rolling mill to produce an intermediate billet. The thickness of the continuously cast billet is 230 mm, and the thickness of the intermediate billet is 40 mm. Specific rough rolling process parameters are as follows:

[0073] The roughing horizontal rolling mill includes a first horizontal rolling mill and a second horizontal rolling mill.

[0074] The first horizontal rolling mill has three rolling passes: 24% reduction in the first pass, 21% reduction in the second pass, and 16% reduction in the third pass. The exit temperature of the rolled piece from the first horizontal rolling mill is 1040℃. To improve the surface quality of the rolled piece, high-pressure water descaling is used both when the rolled piece enters and leaves the first horizontal rolling mill.

[0075] Since the rolling width of the workpiece is 1250mm, the second horizontal rolling mill adopts three passes: the first pass has a reduction rate of 34%, the second pass has a reduction rate of 36%, and the third pass has a reduction rate of 18.37%.

[0076] The exit temperature of the rolled piece is 1000℃ at the second horizontal rolling mill. In order to ensure the rolling temperature and final rolling temperature of the second horizontal rolling mill, the rolled piece is only descaled before entering the second horizontal rolling mill.

[0077] S023. Finishing, Laminar Flow Cooling, and Coiling: The intermediate billet obtained from roughing is rolled to a thickness of 3.75 mm after finishing. The final rolling temperature during finishing is 885℃. After finishing, the billet is subjected to laminar flow cooling, specifically front-stage cooling. The opening degree of both the upper and lower manifolds in the front-stage cooling is 75%.

[0078] After laminar cooling, the rolled piece is coiled at a temperature of 659°C to obtain a hot-rolled coil.

[0079] S03, pickling and cold continuous rolling

[0080] The hot-rolled coils obtained after hot rolling are pickled and then placed in a pickling and rolling unit for rolling. The rolling parameters include: the concentration of hydrochloric acid for pickling is 166 g / L, the pickling temperature is 80℃, the elongation of the tension leveler is 2.0%, the cold rolling reduction rate is 76%, the surface roughness of the pickling and rolling S5 stand rolls is 4.0 μm, the unit rolling force of the pickling and rolling S5 stand rolls is 6 MN / m, and the pickling and rolling thickness is 0.912 mm.

[0081] S04, Annealing

[0082] Annealing is performed in a vertical continuous annealing furnace. The pickled and cold-rolled workpiece is placed in the vertical continuous annealing furnace and sequentially passes through the preheating section, heating section, soaking section, slow cooling section, rapid cooling section, over-aging section and final cooling section.

[0083] The preheating section has a temperature of 130℃, the heating section has a temperature of 780℃, the soaking section has a temperature of 782℃, the slow cooling section has a temperature of 650℃, the rapid cooling section has a temperature of 400℃, the over-aging section has a temperature of 380℃, and the final cooling section has a temperature of 180℃.

[0084] S05, leveling and straightening

[0085] The parameters for leveling and tension straightening include: the surface roughness of the leveling work roll is 3.5 μm, the elongation of leveling is 1.2%, and the elongation of tension straightening is 0.1%.

[0086] In this embodiment, the steel used for the fire extinguisher cylinder prepared through the above steps is steel strip. The surface roughness of the steel strip, as measured by a roughness tester, is 0.982 μm. The steel strip is then observed under a scanning electron microscope to obtain the following... Figure 1 The results shown are from Figure 1 It is known that the steel strip structure provided in the embodiments of the present invention consists of ferrite and cementite, with the ferrite content being 94.6%, the cementite content being 5.4%, and the ferrite grain size being 8.5.

[0087] Example 2

[0088] This embodiment provides a method for preparing steel for fire extinguisher cylinders. The specific steps are similar to those in Embodiment 1, with the only difference being:

[0089] In step S021, the heating temperature of the furnace is 1217℃.

[0090] In step S023, the final rolling temperature of the workpiece during finishing rolling is 887℃, and the coiling temperature is 640℃.

[0091] The temperature of the soaking zone in step S04 is 784℃.

[0092] The elongation rate of the smoothing in step S05 is 1.19%.

[0093] In this embodiment, the steel used for the fire extinguisher cylinder obtained through the above steps is steel strip, and the surface roughness of the steel strip is 0.876μm as measured by a roughness tester.

[0094] Example 3

[0095] This embodiment provides a method for preparing steel for fire extinguisher cylinders. The specific steps are similar to those in Embodiment 1, with the only difference being:

[0096] In step S021, the heating temperature of the furnace is 1212℃.

[0097] In step S023, the final rolling temperature of the workpiece during finishing rolling is 883℃, and the coiling temperature is 605℃.

[0098] The temperature of the soaking zone in step S04 is 781℃.

[0099] The elongation rate of the smoothing in step S05 is 1.22%.

[0100] In this embodiment, the steel used for the fire extinguisher cylinder prepared by the above steps is steel strip, and the surface roughness of the steel strip is 0.893μm as measured by a roughness tester.

[0101] Example 4

[0102] This embodiment provides a method for preparing steel for fire extinguisher cylinders, including the following steps:

[0103] S01. Preparation of continuous casting billet

[0104] The existing smelting method involves sequential desulfurization of molten iron, converter smelting, argon blowing of the molten steel, refining in an RH furnace, and then continuous casting into a continuously cast billet. The composition of the continuously cast billet is: C: 0.046%, Mn: 0.19%, S: 0.008%, P: 0.015%, Si: 0.024%, Alt: 0.041%, N: 0.0037%, with the remainder being Fe and other unavoidable impurities: 99.6723%.

[0105] S02, hot rolled

[0106] S021. Heating: Place the continuously cast billet in a heating furnace and heat it to 1223℃.

[0107] S022, Rough Rolling: The heated continuously cast billet is placed in a rough rolling mill to produce an intermediate billet. The thickness of the continuously cast billet is 230 mm, and the thickness of the intermediate billet is 42 mm. Specific rough rolling process parameters are as follows:

[0108] The roughing horizontal rolling mill includes a first horizontal rolling mill and a second horizontal rolling mill.

[0109] The first horizontal rolling mill has three rolling passes: 21% reduction in the first pass, 19% reduction in the second pass, and 17% reduction in the third pass. The exit temperature of the rolled piece from the first horizontal rolling mill is 1020℃. To improve the surface quality of the rolled piece, high-pressure water descaling is used both when the rolled piece enters and leaves the first horizontal rolling mill.

[0110] Since the rolling width of the workpiece is 1350mm, the second horizontal rolling mill adopts a five-pass rolling process. The reduction rate is 21% for the first pass, 22% for the second pass, 21% for the third pass, 21% for the fourth pass, and 10.60% for the fifth pass. The exit temperature of the workpiece in the second horizontal rolling mill is 1020℃. In order to ensure the rolling temperature and finishing temperature of the second horizontal rolling mill, the workpiece is only descaled before entering the second horizontal rolling mill.

[0111] S023. Finishing, Laminar Flow Cooling, and Coiling: The intermediate billet obtained from roughing is rolled to a thickness of 4.0 mm after finishing. The final rolling temperature during finishing is 881℃. After finishing, the billet is subjected to laminar flow cooling, specifically front-stage cooling. The opening degree of both the upper and lower manifolds in the front-stage cooling is 75%.

[0112] After laminar cooling, the rolled piece is coiled at a temperature of 656℃ to obtain a hot-rolled coil.

[0113] S03, pickling and cold continuous rolling

[0114] The hot-rolled coils obtained after hot rolling are pickled and then placed in a pickling and rolling unit for rolling. The rolling parameters include: the concentration of hydrochloric acid for pickling is 170 g / L, the pickling temperature is 78℃, the elongation of the tension leveler is 2.2%, the cold rolling reduction rate is 75%, the surface roughness of the pickling and rolling S5 stand rolls is 3.5 μm, the unit rolling force of the pickling and rolling S5 stand rolls is 6 MN / m, and the pickling and rolling thickness is 1.013 mm.

[0115] S04, Annealing

[0116] Annealing is performed in a vertical continuous annealing furnace. The pickled and cold-rolled workpiece is placed in the vertical continuous annealing furnace and sequentially passes through the preheating section, heating section, soaking section, slow cooling section, rapid cooling section, over-aging section and final cooling section.

[0117] The preheating section has a temperature of 135℃, the heating section has a temperature of 795℃, the soaking section has a temperature of 798℃, the slow cooling section has a temperature of 645℃, the rapid cooling section has a temperature of 405℃, the over-aging section has a temperature of 390℃, and the final cooling section has a temperature of 183℃.

[0118] S05, leveling and straightening

[0119] The parameters for leveling and tension straightening include: the surface roughness of the leveling work roll is 3.5 μm, the elongation of leveling is 1.21%, and the elongation of tension straightening is 0.1%.

[0120] In this embodiment, the steel used for the fire extinguisher cylinder prepared through the above steps is steel strip. The surface roughness of the steel strip, as measured by a roughness tester, is 1.03 μm. The steel strip is then observed under a scanning electron microscope to obtain the following... Figure 2 The results shown are from Figure 2 It is known that the steel strip structure provided in the embodiments of the present invention consists of ferrite and cementite, with the ferrite content being 94.4%, the cementite content being 5.6%, and the ferrite grain size being 8.5.

[0121] Example 5

[0122] This embodiment provides a method for preparing steel for fire extinguisher cylinders. The specific steps are similar to those in Embodiment 1, with the only difference being:

[0123] In step S021, the heating temperature of the furnace is 1226℃.

[0124] In step S023, the final rolling temperature of the workpiece during finishing rolling is 876℃, and the coiling temperature is 645℃.

[0125] The temperature of the soaking zone in step S04 is 796℃.

[0126] In this embodiment, the steel used for the fire extinguisher cylinder prepared by the above steps is steel strip, and the surface roughness of the steel strip is 1.08μm as measured by a roughness tester.

[0127] Example 6

[0128] This embodiment provides a method for preparing steel for fire extinguisher cylinders. The specific steps are similar to those in Embodiment 1, with the only difference being:

[0129] In step S021, the heating temperature of the furnace is 1224℃.

[0130] In step S023, the final rolling temperature of the workpiece during finishing rolling is 875℃, and the coiling temperature is 651℃.

[0131] The temperature of the soaking zone in step S04 is 792℃.

[0132] The elongation rate of the smoothing in step S05 is 1.23%.

[0133] In this embodiment, the steel used for the fire extinguisher cylinder prepared by the above steps is steel strip, and the surface roughness of the steel strip is 1.116μm as measured by a roughness tester.

[0134] Comparative Example 1

[0135] This comparative example provides a method for preparing steel for fire extinguisher cylinders. The specific steps are the same as in Example 1, except that the annealing and homogenization temperature in step S04 is 740℃.

[0136] Comparative Example 2

[0137] This comparative example provides a method for preparing steel for fire extinguisher cylinders. The specific steps are the same as in Example 1, except that the annealing and homogenization temperature in step S04 is 830°C.

[0138] Comparative Example 3

[0139] This comparative example provides a method for preparing steel for fire extinguisher cylinders. The specific steps are the same as in Example 1, except that the final rolling temperature in step S023 is 840℃.

[0140] Comparative Example 4

[0141] This comparative example provides a method for preparing steel for fire extinguisher cylinders. The specific steps are the same as in Example 1, except that the final rolling temperature in step S023 is 910℃.

[0142] Comparative Example 5

[0143] This comparative example provides a method for preparing steel for fire extinguisher cylinders. The specific steps are the same as in Example 1, except that the coiling temperature in step S023 is 570°C.

[0144] Comparative Example 6

[0145] This comparative example provides a method for preparing steel for fire extinguisher cylinders. The specific steps are the same as in Example 1, except that the coiling temperature in step S023 is 720°C.

[0146] Experimental Example 1

[0147] The fire extinguisher cylinder steel prepared by the methods of Examples 1-6 and Comparative Examples 1-6 was subjected to mechanical property testing. The yield strength, tensile strength, and elongation A were obtained through tensile testing. 80 The results are shown in Table 1.

[0148] Table 1 Mechanical properties of steel used for fire extinguisher cylinders

[0149] Yield strength / MPa Tensile strength / MPa Elongation / % Example 1 231 352 38 Example 2 236 356 39 Example 3 241 361 41 Example 4 235 355 39 Example 5 239 358 37 Example 6 246 365 39 Comparative Example 1 282 385 34 Comparative Example 2 205 344 41 Comparative Example 3 290 390 33 Comparative Example 4 200 340 38 Comparative Example 5 285 386 35 Comparative Example 6 208 342 40

[0150] As shown in Table 1, the embodiments of the present invention, by controlling the composition and preparation method of the steel used for fire extinguisher cylinders, produce fire extinguisher cylinder steel with excellent mechanical properties, fully meeting the requirements for fire extinguisher cylinders. When used to prepare fire extinguisher cylinders, it exhibits good formability and weldability, and no dents occur under high-temperature spinning. After being made into fire extinguishers, no leakage or rupture was observed during pressure testing, demonstrating high safety. In Comparative Example 1, the low temperature of the soaking zone during annealing resulted in insufficient ferrite grain growth, leading to a higher yield strength that does not meet the requirements for fire extinguisher steel. In Comparative Example 2, the high temperature of the soaking zone during annealing resulted in excessive ferrite grain growth, leading to lower yield strength and tensile strength that also do not meet the requirements for fire extinguisher steel. In Comparative Example 3, the low final rolling temperature resulted in insufficient recrystallization of hot-rolled ferrite, leading to a higher yield strength that also does not meet the requirements for fire extinguisher steel. Comparative Example 4 had an excessively high final rolling temperature, resulting in excessively large hot-rolled ferrite grains and a low yield strength, failing to meet the requirements for fire extinguisher steel. Comparative Example 5 had an excessively low coiling temperature, resulting in fine hot-rolled ferrite grains and a high yield strength, also failing to meet the requirements for fire extinguisher steel. Comparative Example 6 had an excessively high coiling temperature, resulting in large hot-rolled ferrite grains and a low yield strength, also failing to meet the requirements for fire extinguisher steel.

[0151] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing a steel for fire extinguisher cylinders, characterized in that, The continuous casting billet is sequentially subjected to hot rolling, pickling, cold continuous rolling and annealing; The element composition of the continuous casting billet comprises C: 0.040-0.08%, Mn: 0.15-0.25%, S: ≤0.015%, P: ≤0.025%, Si: ≤0.030%, Al: 0.030-0.060%, N: ≤0.0050%, and the rest is Fe and other inevitable impurities; The hot rolling comprises rough rolling and finish rolling, the finish rolling comprises rolling the intermediate billet obtained by the rough rolling, the finish rolling temperature of the rolled piece is 860-900℃, the rolled piece is subjected to laminar cooling after the finish rolling, and the rolled piece is coiled after the laminar cooling, and the coiling temperature is 600-660℃; The annealing comprises a preheating section, a heating section, a soaking section, a slow cooling section, a fast cooling section, an overaging section and a final cooling section, the preheating section temperature is 130-140℃, the heating section temperature is 750-800℃, the soaking section temperature is 760-800℃, the slow cooling section temperature is 640-660℃, the fast cooling section temperature is 390-410℃, the overaging section temperature is 360-400℃, and the final cooling section temperature is 170-190℃; The metallographic structure of the steel for the fire extinguisher cylinder body is ferrite and cementite, the content of the ferrite is 90-95%, the content of the cementite is 5-10%, and the grain size of the ferrite is 8.0-8.

5.

2. The production method according to claim 1, characterized by, The thickness of the intermediate billet obtained by the rough rolling is 15-20% of the thickness of the continuous casting billet.

3. The preparation method according to claim 1, characterized in that, The horizontal roller mill of the rough rolling comprises a first horizontal roller mill and a second horizontal roller mill, the rolling pass of the first horizontal roller mill is 3 passes, and the rolling pass of the second horizontal roller mill is 3 passes or 5 passes.

4. The production method according to claim 3, characterized by, The reduction parameters of the first horizontal roller mill comprise: the first pass reduction rate is 20-24%, the second pass reduction rate is 18-22%, and the third pass reduction rate is 15-18%.

5. The preparation method according to claim 3, characterized in that, The outlet temperature of the rolled piece from the first horizontal roller mill is 1000-1060℃.

6. The preparation method according to claim 3, characterized in that, The rolled piece is subjected to descaling operation when entering and leaving the first horizontal roller mill.

7. The preparation method according to claim 3, characterized in that, When the rolling pass of the second horizontal roller mill is 3 passes, the reduction parameters comprise: the first pass reduction rate is 29-35%, the second pass reduction rate is 32-38%, and the third pass reduction rate is 16-20%.

8. The preparation method according to claim 3, characterized in that, When the rolling pass of the second horizontal roller mill is 5 passes, the reduction parameters comprise: the first pass reduction rate is 20-24%, the second pass reduction rate is 20-25%, the third pass reduction rate is 20-25%, the fourth pass reduction rate is 20-24%, and the fifth pass reduction rate is 10-15%.

9. The preparation method according to claim 3, characterized in that, When the rolling width of the rolled piece is >1300mm and / or the width reduction of the rolled piece is >50mm, the rolling pass of the second horizontal roller mill is 5 passes.

10. The method of claim 3, wherein, The outlet temperature of the rolled piece from the second horizontal roller mill is 970-1030℃.

11. The preparation method according to claim 3, characterized in that, The rolled piece is subjected to descaling operation before entering the second horizontal roller mill.

12. The method of claim 1, wherein, The rough rolling further comprises heating the continuous casting billet, and the heating temperature is 1200-1240℃.

13. The method of claim 1, wherein, The laminar cooling is front-stage cooling, and the opening degrees of the upper and lower headers are both 70-80%.

14. The method of claim 1, wherein, The pickling cold continuous rolling comprises rolling the rolled piece obtained after hot rolling after pickling.

15. The preparation method according to claim 14, characterized in that, The parameters of the pickling cold continuous rolling process comprise: pickling temperature 75-85 DEG C, stretcher elongation 1.5-2.5%, cold rolling reduction 70-80%, roughness of the S5 rack rolling mill 3.5-4.5 mu m, unit rolling force of the S5 rack rolling mill 5-7 MN / m.

16. The method of claim 1, wherein, The annealed rolled piece is further flattened and straightened, the working roll roughness of the flattening is 3.0-4.0 mu m, the flattening elongation is 0.6-1.3%, and the straightening elongation is 0.03-0.1%.

17. A steel for fire extinguisher cylinders, characterized in that, The steel has a yield strength of 210-280 MPa, a tensile strength of 320-410 MPa, an elongation A 80 ≥ 35 %, a surface roughness Ra of 0.70-1.60 µm.

18. Use of the steel prepared according to the method of any one of claims 1-16 or the steel of claim 17 in the manufacture of fire-fighting steel tools.

Images