1300MPa Grade High-Strength and High-Toughness Seamless Gas Cylinder Steel and Manufacturing Method

Abstract

This application relates to the field of alloy technology, disclosing a 1300MPa grade high-strength, high-toughness seamless gas cylinder steel and its manufacturing method. The chemical composition of the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel, by mass percentage, includes: C: 0.2%~0.3%, Si: 0.25%~0.55%, Mn: 0.8%~1.5%, Cr: 0.7%~1.5%, Mo: 0.3%~0.8%, Ni: 1.0%~1.5%, V: 0.1%~0.3%, Nb: 0.02%~0.05%, P≤0.020%, S≤0.010%, P+S≤0.025%, with the remainder being Fe and unavoidable impurities. In this application, the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel combines high strength with good low-temperature transverse impact toughness.

Description

Technical Field

[0001] This application belongs to the field of alloy technology, specifically relating to a 1300MPa grade high-strength and high-toughness seamless gas cylinder steel and its manufacturing method. Background Technology

[0002] Seamless steel gas cylinders are widely used in industry, medical, aerospace and other fields as the fastest and simplest packaging for storing and transporting flammable and industrial compressed gases. Domestic production of seamless steel pipes for gas cylinders mainly follows the GB / T18248-2021 standard. Commonly used cylinder materials are 30CrMo and 34CrMo4. After heat treatment, the maximum tensile strength generally does not exceed 1000MPa, and the working pressure is generally within 20MPa.

[0003] In recent years, high-pressure gas cylinders with a working pressure of 30MPa have begun to be used. The wall thickness of these cylinders is significantly thinner than those made with ordinary materials. This not only achieves weight reduction, saves resources, and reduces losses during transportation and handling, but most importantly, it greatly increases the gas capacity of a single cylinder, providing favorable conditions for gas use. The steel used in these cylinders is manufactured according to the ISO 9809-2:2010 standard, which specifies the following mechanical properties: tensile strength ≥1100MPa, elongation ≥12%, and transverse impact toughness akv at -50℃ of 30~60 J·cm. -2 .

[0004] Currently, the strength of seamless steel pipes used in 30MPa high-pressure gas cylinders is generally less than 1200MPa, indicating low strength and poor low-temperature impact toughness. For example, a seamless steel pipe for high-pressure gas cylinders, its manufacturing method, and its application are described in related technologies. The performance characteristics of this seamless steel pipe are: tensile strength 1100~1180MPa, yield strength ≥990MPa, elongation ≥13%, and transverse impact value AKv≥60J at -50℃. Summary of the Invention

[0005] This application aims to address at least one of the technical problems existing in the related art.

[0006] Therefore, the first aspect of this application provides a 1300MPa grade high-strength, high-toughness seamless gas cylinder steel.

[0007] The second aspect of this application provides a method for manufacturing 1300MPa grade high-strength, high-toughness seamless gas cylinder steel.

[0008] In view of the above, according to a first aspect of the embodiments of this application, a 1300MPa grade high-strength, high-toughness seamless gas cylinder steel is proposed, the chemical composition of which, by mass percentage, includes: C: 0.2%~0.3%, Si: 0.25%~0.55%, Mn: 0.8%~1.5%, Cr: 0.7%~1.5%, Mo: 0.3%~0.8%, Ni: 1.0%~1.5%, V: 0.1%~0.3%, Nb: 0.02%~0.05%, P≤0.020%, S≤0.010%, P+S≤0.025%, with the remainder being Fe and unavoidable impurities; wherein, the properties of the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel are: yield strength ≥1250MPa, tensile strength ≥1330MPa, elongation after fracture ≥12%, and room temperature transverse impact toughness ≥95J·cm. -2 Transverse impact toughness at -50℃ ≥85 J·cm -2 .

[0009] In one possible implementation, the microstructure of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel includes tempered sorbite, which comprises a ferrite matrix and fine-grained carbides dispersed on the ferrite matrix; the grain size of the reconstructed original austenite in the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel is less than 5μm.

[0010] In one possible implementation, the fine-grained carbides include a first type of carbide and a second type of carbide; the first type of carbide has a chemical composition including Mn and Cr, and an average particle size of 20 nm to 70 nm; the second type of carbide has a chemical composition including Mo and V, and an average particle size of 5 nm to 50 nm.

[0011] According to a second aspect of the embodiments of this application, a method for manufacturing 1300MPa grade high-strength and high-toughness seamless gas cylinder steel is proposed, comprising the following steps: preparing a steel billet; hot rolling the steel billet by 6 to 10 passes of rolling, with an initial rolling temperature of 1140°C to 1160°C and a final rolling temperature of 900°C to 960°C, followed by air cooling to room temperature to obtain a hot-rolled steel billet; quenching the hot-rolled steel billet by holding it at 820°C to 870°C for 0.5 to 1.5 hours, followed by water cooling to room temperature to obtain a quenched metal; and tempering the quenched metal at a tempering temperature of 500°C to 600°C to obtain 1300MPa grade high-strength and high-toughness seamless gas cylinder steel.

[0012] In one possible implementation, during the hot rolling process of the billet, the single-pass reduction rate is less than or equal to 30%.

[0013] In one possible implementation, the thickness of the hot-rolled steel billet is 4 mm to 7 mm.

[0014] In one possible implementation, prior to the hot rolling step of the steel billet, the manufacturing method of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel further includes: heating the steel billet to 1180°C to 1220°C and holding it at that temperature for 2 to 4 hours.

[0015] In one possible implementation, the tempering process of the quenched metal involves holding it at room temperature for 1.5 to 2.5 hours and then air cooling it to room temperature.

[0016] In one possible implementation, the steps for preparing the steel billet include: preparing raw materials according to the chemical composition and proportion of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel as described above; and vacuum smelting the raw materials to obtain the steel billet.

[0017] In one possible implementation, the microstructure of the hot-rolled steel billet comprises lath martensite; in the step of quenching the hot-rolled steel billet, the microstructure of the metal obtained after holding at a temperature of 820°C to 870°C for 0.5h to 1.5h comprises a fully austenitic microstructure; after water cooling to room temperature, the microstructure of the quenched metal obtained comprises quenched martensite; the microstructure of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel comprises tempered sorbite.

[0018] The 1300MPa grade high-strength, high-toughness seamless gas cylinder steel and manufacturing method provided in this application can achieve at least the following technical effects:

[0019] In this application, the chemical composition of the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel, by mass percentage, includes: C: 0.2%~0.3%, Si: 0.25%~0.55%, Mn: 0.8%~1.5%, Cr: 0.7%~1.5%, Mo: 0.3%~0.8%, Ni: 1.0%~1.5%, V: 0.1%~0.3%, Nb: 0.02%~0.05%, P≤0.020%, S≤0.010%, P+S≤0.025%, with the remainder being Fe and unavoidable impurities. The performance of the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel is as follows: yield strength ≥1250MPa, tensile strength ≥1330MPa, elongation after fracture ≥12%, and room temperature transverse impact toughness ≥95J·cm. -2 Transverse impact toughness at -50℃ ≥85 J·cm -2In other words, the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel combines high strength with good low-temperature transverse impact toughness, exhibiting promising application prospects and value. The synergistic effect of C (0.2%~0.3%), Nb (0.02%~0.05%), and V (0.1%~0.3%) ensures that in a low-carbon system, C atoms have a high affinity for Nb and V, preferentially forming dispersed carbides (NbC, VC). Due to the lower carbon content, the carbides are smaller and more uniformly distributed, effectively pinning dislocations and grain boundaries. The precipitation of nano-sized NbC and VC significantly hinders dislocation movement, compensating for the solid solution strengthening loss caused by the reduced C content, thus achieving precipitation strengthening. Nb and V exist as carbonitrides during austenitization and rolling, pinning austenite grain boundaries, inhibiting recrystallization, refining the final grains, and achieving grain refinement strengthening. Fine grains improve yield strength while maintaining good toughness. In summary, this embodiment achieves low-carbon, high-strength through a synergistic design of "reduced carbon content + microalloying." Specifically, it strengthens strength through grain refinement and precipitation enhancement of the C-Nb-V system, maintaining a low carbon content to improve toughness while significantly increasing strength through the precipitation strengthening and grain refinement effects of Nb and V. Furthermore, low-temperature impact toughness is improved by using Ni at 1.0%~1.5%.

[0020] The above general description and the description below are exemplary and illustrative only and are not intended to limit this application. Attached Figure Description

[0021] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations and drawings do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are shown as similar elements. The drawings are not to be scaled. And wherein:

[0022] Figure 1 A flowchart illustrating the manufacturing method of 1300MPa grade high-strength and high-toughness seamless gas cylinder steel provided in this embodiment of the disclosure;

[0023] Figure 2 This is a process diagram of billet heating, hot rolling, quenching and tempering in Example 1;

[0024] Figure 3 The tensile curve of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel of Example 1 is shown.

[0025] Figure 4 The microstructure diagrams are of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel of Example 1, where (a) is a metallographic diagram and (b) is a morphological diagram.

[0026] Figure 5The images show the impact fracture morphology of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel of Example 1, where (c) is the impact fracture morphology at room temperature and (d) is the impact fracture morphology at -50℃. Detailed Implementation

[0027] To provide a more detailed understanding of the features and technical content of the embodiments of this disclosure, the implementation of the embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. The accompanying drawings are for illustrative purposes only and are not intended to limit the embodiments of this disclosure. In the following technical description, for ease of explanation, several details are used to provide a full understanding of the disclosed embodiments. However, one or more embodiments may still be implemented without these details.

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the present disclosure can be combined with each other.

[0029] This disclosure discloses a 1300MPa grade high-strength, high-toughness seamless gas cylinder steel. Its chemical composition, by mass percentage, includes: C: 0.2%~0.3%, Si: 0.25%~0.55%, Mn: 0.8%~1.5%, Cr: 0.7%~1.5%, Mo: 0.3%~0.8%, Ni: 1.0%~1.5%, V: 0.1%~0.3%, Nb: 0.02%~0.05%, P≤0.020%, S≤0.010%, P+S≤0.025%, with the remainder being Fe and unavoidable impurities. The 1300MPa grade high-strength, high-toughness seamless gas cylinder steel exhibits the following properties: yield strength ≥1250MPa, tensile strength ≥1330MPa, elongation after fracture ≥12%, and room temperature transverse impact toughness ≥95 J·cm. -2 Transverse impact toughness at -50℃ ≥85 J·cm -2 .

[0030] In this embodiment, the chemical composition of the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel, by mass percentage, includes: C: 0.2%~0.3%, Si: 0.25%~0.55%, Mn: 0.8%~1.5%, Cr: 0.7%~1.5%, Mo: 0.3%~0.8%, Ni: 1.0%~1.5%, V: 0.1%~0.3%, Nb: 0.02%~0.05%, P≤0.020%, S≤0.010%, P+S≤0.025%, with the remainder being Fe and unavoidable impurities. The resulting 1300MPa grade high-strength, high-toughness seamless gas cylinder steel exhibits the following properties: yield strength ≥1250MPa, tensile strength ≥1330MPa, elongation after fracture ≥12%, and room temperature transverse impact toughness ≥95 J·cm. -2Transverse impact toughness at -50℃ ≥85 J·cm -2 In other words, the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel combines high strength with good low-temperature transverse impact toughness, exhibiting promising application prospects and value. The 1300MPa grade high-strength, high-toughness seamless gas cylinder steel of this embodiment is suitable for high-pressure gas cylinders with a working pressure of 30MPa.

[0031] The synergistic effect of C (0.2%~0.3%), Nb (0.02%~0.05%), and V (0.1%~0.3%) in the low-carbon system results in a high affinity between C atoms and Nb and V, preferentially forming dispersed carbides (NbC, VC). Due to the lower carbon content, the carbides are smaller and more uniformly distributed, effectively pinning dislocations and grain boundaries. The precipitation of nanoscale NbC and VC significantly hinders dislocation movement, compensating for the loss of solid solution strengthening caused by the reduction in C content, thus achieving precipitation strengthening and significantly improving the strength of the steel. Nb and V exist as carbonitrides during austenitization and rolling, which can pin austenite grain boundaries, inhibit recrystallization, refine the final grains, and achieve grain refinement strengthening. Fine grains improve yield strength while maintaining good toughness. In summary, this embodiment achieves low-carbon, high-strength through a synergistic design of "reduced carbon content + microalloying." Specifically, it strengthens strength through grain refinement and precipitation enhancement of the C-Nb-V system, maintaining a low carbon content to improve toughness while significantly increasing strength through the precipitation strengthening and grain refinement effects of Nb and V. Furthermore, low-temperature impact toughness is improved by using Ni at 1.0%~1.5%.

[0032] More specifically:

[0033] Carbon (C): 0.2%~0.3%, is the main element for achieving the strength of seamless gas cylinder steel with high strength and high toughness of 1300MPa grade. This embodiment considers that if the carbon content is too low, the strength requirements cannot be met. If excessive carbon is used, brittle phases are easily formed, impairing the toughness of the steel. This embodiment achieves increased strength by using a C content of 0.2%~0.3%.

[0034] Silicon (Si): 0.25%~0.55%, plays a role in solid solution strengthening, increasing the strength of steel. Furthermore, silicon can react with oxides to form silicon dioxide, creating a protective film that improves the corrosion resistance of the steel.

[0035] Using manganese (Mn) as a ferrite-strengthening element, this embodiment takes into account that manganese will promote the segregation of harmful elements at grain boundaries and increase the temper brittleness of steel. Therefore, solid solution strengthening is achieved by using manganese (Mn) at a concentration of 0.8%~1.5%, and the hardenability of steel is improved.

[0036] In this embodiment, considering that chromium promotes the segregation of impurity atoms in steel, which exacerbates the temper brittleness of steel, a chromium (Cr) content of 0.7%~1.5% is used to achieve the formation of stable carbides during tempering, which are less prone to growth, thus refining the grain size and improving the uniformity of the carbides.

[0037] Molybdenum (Mo): 0.3%~0.8%, can dissolve in ferrite, playing a role in solid solution strengthening. Molybdenum is also a strong carbide-forming element, precipitating carbides during tempering, refining grains, and at the same time, it can hinder the growth of Nb, V and other carbides, refine the precipitated phase, and promote tempering stability.

[0038] Nickel (Ni): 1.0%~1.5%, can strengthen ferrite and lower the ductile-brittle transition temperature. At the same time, nickel can effectively reduce the resistance to dislocation movement, thereby enhancing the strength of steel while improving its low-temperature toughness.

[0039] Vanadium (V): 0.1%~0.3%, is a strong carbide-forming element. During tempering, it precipitates to form carbonitrides, playing a precipitation strengthening role and improving low-temperature impact toughness. In addition, VC particles have a high dissolution temperature, which can effectively prevent grain boundary movement and has a good grain refinement effect.

[0040] Niobium (Nb): 0.02%~0.05%, precipitates during tempering to form carbonitrides. Fine Nb(C,N) particles (i.e., niobium carbonitrides) pin the austenite grain boundaries, preventing grain boundary movement and inhibiting dynamic recrystallization of the steel. If dynamic recrystallization occurs during deformation, the resulting grain boundary migration can enclose microcracks formed at the original grain boundaries within new grains, preventing crack aggregation, growth, and extension, thus improving the steel's ductility.

[0041] Phosphorus (P) ≤ 0.020%, sulfur (S) ≤ 0.010%, and the sum of P and S content (P+S) ≤ 0.025% help to achieve both high strength and high toughness in 1300MPa grade high-strength and high-toughness seamless gas cylinder steel.

[0042] In some embodiments, the microstructure of the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel includes tempered sorbite, which comprises a ferrite matrix and fine-grained carbides dispersed in the ferrite matrix. The grain size of the reconstructed original austenite in the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel is less than 5μm.

[0043] In this embodiment, the tempered sorbite microstructure consists of a ferrite matrix and fine-grained carbides dispersed on the ferrite matrix. The microstructure of the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel is tempered sorbite. The grain size of the reconstructed original austenite in the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel is less than 5μm, forming a system of fine-grain strengthening + precipitation strengthening + microstructure optimization. This achieves a yield strength ≥1250MPa, tensile strength ≥1330MPa, elongation after fracture ≥12%, and room temperature transverse impact toughness ≥95J·cm for the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel. -2 Transverse impact toughness at -50℃ ≥85 J·cm -2 That is, it has high strength and good low-temperature impact toughness. Seamless gas cylinders made of 1300MPa grade high-strength and high-toughness seamless gas cylinder steel can withstand high internal pressure, such as a working pressure of 30MPa.

[0044] In some embodiments, the fine-grained carbides include a first type of carbide and a second type of carbide; the first type of carbide has a chemical composition including Mn and Cr, and an average particle size of 20 nm to 70 nm; the second type of carbide has a chemical composition including Mo and V, and an average particle size of 5 nm to 50 nm.

[0045] In other words, the fine-grained carbides in the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel mainly include Mn and Cr carbides with an average particle size of 20nm to 70nm, and Mo and V carbides with an average particle size of 5nm to 50nm. These Mn and Cr carbides with an average particle size of 20nm to 70nm, and Mo and V carbides with an average particle size of 5nm to 50nm, synergistic precipitation strengthening achieves high strength, inhibits grain growth and stabilizes the microstructure to achieve high toughness, and also exhibits good thermal stability. Thus, the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel simultaneously possesses high strength, excellent low-temperature toughness, and good microstructural thermal stability.

[0046] Combination Figure 1 As shown in the embodiments of this disclosure, a method for manufacturing 1300MPa grade high-strength, high-toughness seamless gas cylinder steel is provided, comprising the following steps:

[0047] S1. Prepare steel billets.

[0048] By preparing steel billets, a basic material is provided for subsequent processing.

[0049] In some embodiments, the step of preparing the steel billet includes: preparing raw materials according to the chemical composition and proportion of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel as described above; and performing vacuum smelting on the raw materials to obtain the steel billet.

[0050] Vacuum smelting of raw materials improves the purity of steel billets, laying the foundation for subsequent processing.

[0051] S2. The steel billet is hot-rolled in 6 to 10 passes, with an initial rolling temperature of 1140°C to 1160°C and a final rolling temperature of 900°C to 960°C. It is then air-cooled to room temperature to obtain a hot-rolled steel billet.

[0052] By performing 6 to 10 rolling passes, with an initial rolling temperature of 1140°C to 1160°C and a final rolling temperature of 900°C to 960°C, followed by air cooling to room temperature, grain refinement is achieved, resulting in a microstructure of hot-rolled steel billets including lath martensite.

[0053] In one possible implementation, the steel billet is hot-rolled in 6, 8, or 10 passes.

[0054] In some embodiments, during the hot rolling process of the steel billet, the single-pass reduction rate is less than or equal to 30%.

[0055] By performing 6 to 10 rolling passes with a single-pass reduction of less than or equal to 30%, an initial rolling temperature of 1140°C to 1160°C, a final rolling temperature of 900°C to 960°C, and air cooling to room temperature, grain refinement is achieved, resulting in a uniform and fine deformed structure, thus improving the uniformity of strength and toughness.

[0056] In some embodiments, the thickness of the hot-rolled steel billet is 4 mm to 7 mm.

[0057] By using hot-rolled steel billets with a thickness of 4mm to 7mm, a fine and uniform initial microstructure is provided to prepare for subsequent quenching treatment, thus enabling a full martensitic transformation and laying the foundation for obtaining high strength and toughness.

[0058] S3. The hot-rolled steel billet is quenched at 820℃ to 870℃ for 0.5h to 1.5h and then water-cooled to room temperature to obtain quenched metal.

[0059] Specifically, the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel includes austenite-stabilizing elements and microalloying elements. For example, austenite-stabilizing elements such as C (0.2%~0.3%), Mn (0.8%~1.5%), and Ni (1.0%~1.5%) can lower the austenite transformation temperature (Ac1 to Ac3) and expand the austenite stability range, thus achieving a wider quenching temperature range. Furthermore, the precipitates formed by microalloying elements such as V (0.1%~0.3%) and Nb (0.02%~0.05%) can inhibit grain growth and pin austenite grain boundaries, reducing high-temperature sensitivity. Moreover, the multi-pass hot rolling process before quenching results in a fine and uniform microstructure. During heating, there are many austenite nucleation sites and the transformation is uniform. In addition, the nanoprecipitates can pin the austenite grains, resulting in finer austenite grains. This reduces the sensitivity to overheating and achieves the insensitivity of quenching temperature to 1300MPa grade high-strength and high-toughness seamless gas cylinder steel.

[0060] This embodiment takes into account that traditional gas cylinder steel production uses a high quenching temperature above 870℃, which results in coarse austenite size and compromises toughness. Therefore, since 1300MPa grade high-strength, high-toughness seamless gas cylinder steel is not sensitive to quenching temperature, this embodiment obtains a hard-phase quenched martensite structure by holding the steel at 820℃ to 870℃ for 0.5h to 1.5h, followed by water cooling to room temperature. This water quenching provides the microstructure conditions for achieving high strength and high toughness.

[0061] In one possible implementation, the quenching temperature is 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, or other temperatures between 820°C and 870°C.

[0062] For example, the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel of this embodiment also achieves excellent performance after quenching at 820℃. Compared with related technologies, this reduces the quenching temperature, decreases energy consumption during processing, and saves resources.

[0063] S4. Temper the quenched metal at a temperature of 500℃ to 600℃ to obtain 1300MPa grade high-strength and high-toughness seamless gas cylinder steel.

[0064] By tempering at a temperature of 500℃ to 600℃, a 1300MPa grade high-strength and high-toughness seamless gas cylinder steel is obtained, which makes the microstructure of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel include tempered sorbite structure, thereby improving strength and toughness.

[0065] In some embodiments, in the step of tempering the quenched metal, the holding time is 1.5h to 2.5h, and then the metal is air-cooled to room temperature.

[0066] By holding the material for 1.5 to 2.5 hours and then air-cooling it to room temperature, the uniformity of the tissue and properties is improved, and fine-grained carbide reinforcement is achieved.

[0067] In this embodiment, the manufacturing method employs a traditional hot rolling + quenching + tempering process, which is simple. Specifically, hot rolling provides a fine and uniform initial microstructure. Since the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel is insensitive to quenching temperature, a hard-phase quenched martensite microstructure is obtained after water quenching at 820℃ to 870℃ for 0.5h to 1.5h. The tempering temperature range is relatively wide, ranging from 500℃ to 600℃, achieving a yield strength ≥1250MPa, tensile strength ≥1330MPa, and room temperature transverse impact toughness akv ≥95J·cm for the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel. -2 Transverse impact toughness at -50℃ akv ≥ 85 J·cm -2 .

[0068] In practical applications, the strength index can be adjusted by tempering temperature to meet the performance requirements of gas cylinders for different purposes.

[0069] In some embodiments, prior to the hot rolling process of the billet, the method for manufacturing 1300MPa grade high-strength and high-toughness seamless gas cylinder steel further includes: heating the billet to 1180°C to 1220°C and holding it at that temperature for 2 hours to 4 hours.

[0070] Before hot rolling, the steel billet is heated to 1180°C to 1220°C and held for 2 to 4 hours to obtain a uniform and suitable microstructure for hot rolling.

[0071] For example, a steel billet is prepared. First, the steel billet is heated to 1180°C to 1220°C and held at that temperature for 2 to 4 hours. Then, the steel billet is hot-rolled in 6 to 10 passes, with an initial rolling temperature of 1140°C to 1160°C and a final rolling temperature of 900°C to 960°C. It is then air-cooled to room temperature to obtain a hot-rolled steel billet.

[0072] In some embodiments, the microstructure of the hot-rolled steel billet comprises lath martensite. In the quenching process of the hot-rolled steel billet, the billet is held at 820°C to 870°C for 0.5 to 1.5 hours, resulting in a metal microstructure comprising full austenite. Water cooling to room temperature yields a quenched metal microstructure comprising quenched martensite. The microstructure of the 1300 MPa grade high-strength, high-toughness seamless gas cylinder steel comprises tempered sorbite.

[0073] The microstructure of the hot-rolled steel billet includes lath martensite to obtain a high-strength initial microstructure. Through a quenching process at 820℃ to 870℃ for 0.5h to 1.5h, the resulting metal microstructure comprises a fully austenitic microstructure, achieving a reconstructed original austenite grain size of less than 5μm for the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel. Water cooling to room temperature results in a quenched metal microstructure comprising quenched martensite to obtain high strength and form tempering precursors. After tempering, the microstructure of the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel comprises tempered sorbite, achieving a good balance of strength and toughness, resulting in a stable microstructure. The properties of seamless gas cylinder steel with high strength and high toughness of 1300MPa grade are as follows: yield strength ≥1250MPa, tensile strength ≥1330MPa, elongation after fracture ≥12%, and room temperature transverse impact toughness ≥95J·cm. -2 Transverse impact toughness at -50℃ ≥85 J·cm -2 .

[0074] Example 1:

[0075] A 1300MPa grade high-strength, high-toughness seamless gas cylinder steel, the chemical composition of which, by mass percentage, includes: C: 0.25%, Si: 0.32%, Mn: 0.8%, Cr: 1%, Mo: 0.8%, V: 0.13%, Ni: 1.2%, Nb: 0.04%, P≤0.020%, S≤0.010%, P+S≤0.025%, with the balance being Fe and unavoidable impurities.

[0076] A method for manufacturing 1300MPa grade high-strength and high-toughness seamless gas cylinder steel includes the following steps:

[0077] Prepare raw materials according to the chemical composition and proportion of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel of this embodiment.

[0078] The raw materials are vacuum smelted to obtain a steel billet with a thickness × width of 80mm × 80mm.

[0079] Combination Figure 2 As shown, the steel billet is fed into a heating furnace and heated to the complete austenitization temperature of 1200℃, and held for 2 hours.

[0080] Combination Figure 2 As shown, the steel billet after exiting the furnace is hot-rolled. The initial rolling temperature is 1160℃, and the billet thickness is reduced from 80mm to 7.5mm through 8 passes. The reduction rate per pass is less than or equal to 30%. The final rolling temperature is 960℃, and the billet is air-cooled to room temperature to obtain the hot-rolled steel billet. The microstructure of the hot-rolled steel billet includes lath martensite. For example... Figure 2As shown, the thickness of the steel billet starts from 80mm. After each of the eight hot rolling processes, the thickness of the steel billet is as follows: 56mm, 39mm, 27mm, 20mm, 15mm, 12mm, 9mm, and 7.5mm.

[0081] Combination Figure 2 As shown, the hot-rolled steel billet is subjected to quenching treatment. Specifically, the hot-rolled steel billet is placed in an electric arc furnace at a temperature of 820℃ and held for 1 hour to perform complete austenitization treatment. Then, it is water quenched to room temperature to obtain quenched metal. The microstructure of the quenched metal includes quenched martensite.

[0082] Combination Figure 2 As shown, the quenched metal is subjected to tempering treatment. Specifically, the quenched metal is placed in an electric arc furnace at a temperature of 590℃, tempered and held for 2 hours, and then air-cooled to room temperature to obtain 1300MPa grade high-strength and high-toughness seamless gas cylinder steel.

[0083] The tensile curve of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel obtained in Example 1 is as follows: Figure 3 As shown, its performance indicators are as follows: yield strength of 1254 MPa, tensile strength of 1339 MPa, elongation after fracture of 13.9%, and room temperature transverse impact toughness akv of 110 J·cm. -2 The transverse impact toughness akv at -50℃ is 104 J·cm. -2 .

[0084] The microstructure of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel obtained in Example 1 is shown in the figure below. Figure 4 As shown, where, Figure 4 (a) is a metallographic diagram. Figure 4 (b) is a morphology diagram. Microstructural analysis revealed that the microstructure of the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel obtained in Example 1 is tempered sorbite. Specifically, as... Figure 4 As shown in (a), arrow A points to ferrite, and arrow B points to fine-grained carbides. That is, the tempered sorbite structure consists of a ferrite matrix and fine-grained carbides dispersed on the ferrite matrix.

[0085] The impact fracture morphology of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel obtained in Example 1 is as follows: Figure 5 As shown, where, Figure 5 (c) shows the impact fracture morphology at room temperature. Figure 5 (d) is the impact fracture morphology at -50℃. Figure 5 In the diagram, arrow C points to dimples, and arrow D points to tear ridges. According to... Figure 5 It can be seen that the impact fracture morphology of 1300MPa grade high-strength and high-toughness seamless gas cylinder steel is mainly composed of dimples and tear ridges, which have good strength and toughness.

[0086] Example 2:

[0087] A 1300MPa grade high-strength, high-toughness seamless gas cylinder steel, the chemical composition of which, by mass percentage, includes: C: 0.23%, Si: 0.3%, Mn: 1%, Cr: 0.9%, Mo: 0.6%, V: 0.15%, Ni: 1.5%, Nb: 0.03%, P≤0.020%, S≤0.010%, P+S≤0.025%, with the balance being Fe and unavoidable impurities.

[0088] A method for manufacturing 1300MPa grade high-strength and high-toughness seamless gas cylinder steel includes the following steps:

[0089] Prepare raw materials according to the chemical composition and proportion of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel of this embodiment.

[0090] The raw materials are vacuum smelted to obtain a steel billet with a thickness × width of 80mm × 80mm.

[0091] The steel billet is fed into a heating furnace and heated to the complete austenitization temperature of 1200℃, and held for 2 hours.

[0092] The steel billet after exiting the furnace is hot-rolled at an initial rolling temperature of 1150℃. Through eight passes, the billet thickness is reduced from 80mm to 6.2mm, with a single-pass reduction rate of less than or equal to 30%. The final rolling temperature is 940℃, followed by air cooling to room temperature to obtain the hot-rolled steel billet. The microstructure of the hot-rolled steel billet consists of lath martensite.

[0093] The hot-rolled steel billet is subjected to quenching treatment. Specifically, the hot-rolled steel billet is placed in an electric arc furnace at a temperature of 850℃ and held for 1 hour to carry out complete austenitization treatment. Then, it is water quenched to room temperature to obtain quenched metal. The microstructure of the quenched metal includes quenched martensite.

[0094] The quenched metal is tempered by placing it in an electric arc furnace at 550℃ for 2 hours and then air-cooling it to room temperature to obtain 1300MPa grade high-strength and high-toughness seamless gas cylinder steel.

[0095] Mechanical property testing revealed the following performance indicators for the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel obtained in Example 2: yield strength of 1256MPa, tensile strength of 1348MPa, elongation after fracture of 13.8%, and room temperature transverse impact toughness akv of 95.6 J·cm. -2 The transverse impact toughness akv at -50℃ is 90.3 J·cm. -2 .

[0096] According to the analysis, the microstructure of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel obtained in Example 2 is tempered sorbite.

[0097] Example 3:

[0098] A 1300MPa grade high-strength, high-toughness seamless gas cylinder steel, the chemical composition of which, by mass percentage, includes: C: 0.21%, Si: 0.32%, Mn: 1.2%, Cr: 1%, Mo: 0.5%, V: 0.12%, Ni: 1.5%, Nb: 0.02%, P≤0.020%, S≤0.010%, P+S≤0.025%, with the balance being Fe and unavoidable impurities.

[0099] A method for manufacturing 1300MPa grade high-strength and high-toughness seamless gas cylinder steel includes the following steps:

[0100] Prepare raw materials according to the chemical composition and proportion of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel of this embodiment.

[0101] The raw materials are vacuum smelted to obtain a steel billet with a thickness × width of 80mm × 80mm.

[0102] The steel billet is fed into a heating furnace and heated to the complete austenitization temperature of 1200℃, and held for 2 hours.

[0103] The steel billet after exiting the furnace is hot-rolled at an initial rolling temperature of 1160℃. Through eight passes, the billet thickness is reduced from 80mm to 6.5mm, with a single-pass reduction rate of less than or equal to 30%. The final rolling temperature is 930℃, followed by air cooling to room temperature to obtain the hot-rolled steel billet. The microstructure of the hot-rolled steel billet consists of lath martensite.

[0104] The hot-rolled steel billet is subjected to quenching treatment. Specifically, the hot-rolled steel billet is placed in an electric arc furnace at a temperature of 870℃ and held for 1 hour to perform complete austenitization treatment. Then, it is water quenched to room temperature to obtain quenched metal. The microstructure of the quenched metal includes quenched martensite.

[0105] The quenched metal is tempered by placing it in an electric arc furnace at 500℃ for 2 hours and then air-cooling it to room temperature to obtain 1300MPa grade high-strength and high-toughness seamless gas cylinder steel.

[0106] The mechanical properties of the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel obtained in Example 3 are as follows: yield strength of 1275MPa, tensile strength of 1330MPa, elongation after fracture of 13.4%, and room temperature transverse impact toughness akv of 100J·cm. -2 The transverse impact toughness akv at -50℃ is 86.9 J·cm. -2 .

[0107] According to the analysis, the microstructure of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel obtained in Example 3 is tempered sorbite.

[0108] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A 1300MPa grade high-strength, high-toughness seamless gas cylinder steel, characterized in that, The chemical composition, by mass percentage, includes: C: 0.2%~0.3%, Si: 0.25%~0.55%, Mn: 0.8%~1.5%, Cr: 0.7%~1.5%, Mo: 0.3%~0.8%, Ni: 1.0%~1.5%, V: 0.1%~0.3%, Nb: 0.02%~0.05%, P≤0.020%, S≤0.010%, P+S≤0.025%, with the remainder being Fe and unavoidable impurities; The properties of the 1300MPa grade high-strength, high-toughness seamless gas cylinder steel are as follows: yield strength ≥1250MPa, tensile strength ≥1330MPa, elongation after fracture ≥12%, and room temperature transverse impact toughness ≥95J·cm. -2 Transverse impact toughness at -50℃ ≥85 J·cm -2 ; The microstructure of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel includes tempered sorbite, which comprises a ferrite matrix and fine-grained carbides dispersed on the ferrite matrix. The fine-grained carbides include first-type carbides and second-type carbides; The chemical composition of the first type of carbide includes Mn and Cr, and the average particle size of the first type of carbide is 20 nm to 70 nm; The chemical composition of the second type of carbide includes Mo and V, and the average particle size of the second type of carbide is 5 nm to 50 nm; The 1300MPa grade high-strength, high-toughness seamless gas cylinder steel is manufactured in the following manner: Prepare raw materials according to the chemical composition and proportion of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel; The raw material is subjected to vacuum smelting to obtain a steel billet; The steel billet is hot-rolled in 6 to 10 passes at an initial rolling temperature of 1140°C to 1160°C and a final rolling temperature of 900°C to 960°C, and then air-cooled to room temperature to obtain a hot-rolled steel billet. The hot-rolled steel billet is quenched at 820°C to 870°C for 0.5 to 1.5 hours and then water-cooled to room temperature to obtain quenched metal. The quenched metal is tempered at a temperature of 500°C to 600°C to obtain 1300MPa grade high-strength and high-toughness seamless gas cylinder steel.

2. The 1300MPa grade high-strength, high-toughness seamless gas cylinder steel according to claim 1, characterized in that, The reconstructed original austenite grain size of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel is less than 5μm.

3. The 1300MPa grade high-strength, high-toughness seamless gas cylinder steel according to claim 1, characterized in that, In the hot rolling process of the steel billet, the single-pass reduction rate is less than or equal to 30%.

4. The 1300MPa grade high-strength, high-toughness seamless gas cylinder steel according to claim 1, characterized in that, The thickness of the hot-rolled steel billet is 4 mm to 7 mm.

5. The 1300MPa grade high-strength, high-toughness seamless gas cylinder steel according to claim 1, characterized in that, Prior to the hot rolling process of the steel billet, the manufacturing method of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel further includes: The steel billet is heated to 1180°C to 1220°C and held at that temperature for 2 to 4 hours.

6. The 1300MPa grade high-strength, high-toughness seamless gas cylinder steel according to claim 1, characterized in that, In the step of tempering the quenched metal, the holding time is 1.5h to 2.5h, and then it is air-cooled to room temperature.

7. The 1300MPa grade high-strength, high-toughness seamless gas cylinder steel according to claim 1, characterized in that, The microstructure of the hot-rolled steel billet includes lath martensite; In the step of quenching the hot-rolled steel billet, after holding at a temperature of 820°C to 870°C for 0.5h to 1.5h, the microstructure of the metal obtained includes a fully austenitic structure; after water cooling to room temperature, the microstructure of the quenched metal obtained includes a quenched martensite structure. The microstructure of the 1300MPa grade high-strength and high-toughness seamless gas cylinder steel includes tempered sorbite.

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