CN120758803B

CN120758803B - Low-carbon steel for seamless gas cylinder, and preparation method and application thereof

Info

Publication number: CN120758803B
Application number: CN202511244356.4A
Authority: CN
Inventors: 陈鹏; 王勇; 孙群峰; 朱林; 刘继林; 李云杰; 袁国; 张宇婷; 李海平; 刘晓; 彭先明; 韩福龙
Original assignee: Hengyang Valin Steel Tube Co Ltd
Current assignee: Hengyang Valin Steel Tube Co Ltd
Priority date: 2025-09-02
Filing date: 2025-09-02
Publication date: 2025-12-02
Anticipated expiration: 2045-09-02
Also published as: CN120758803A

Abstract

This invention provides a seamless low-carbon steel for gas cylinders, its preparation method, and its application. The preparation method includes: Step S1, preparing raw materials according to the composition of the seamless low-carbon steel for gas cylinders; Step S2, smelting the raw materials to obtain a first steel billet; heat-treating the first steel billet to obtain a second steel billet; Step S3, hot-rolling the second steel billet at least eight times under conditions of an initial rolling temperature of 1120℃~1180℃ and a final rolling temperature of 880℃~980℃ to obtain a hot-rolled steel billet; Step S4, cooling the hot-rolled steel billet to obtain a third steel billet; Step S5, heat-treating the third steel billet to obtain the seamless low-carbon steel for gas cylinders. This invention carefully designs the alloy element composition of the seamless low-carbon steel for gas cylinders, and coordinates it with the preparation process, which not only optimizes the comprehensive mechanical properties of the obtained low-carbon steel, but more importantly, enables it to exhibit excellent impact toughness under low-temperature conditions.

Description

Low-carbon steel for seamless gas cylinder, and preparation method and application thereof

Technical Field

The invention relates to the field of low carbon steel, in particular to low carbon steel for a seamless gas cylinder, a preparation method and application thereof.

Background

Under the current global industrial and energy transformation large background, the steel seamless gas cylinder is used as key pressure-bearing equipment in the fields of industrial gas, medical equipment, aerospace, deep sea exploration and the like, and the improvement of the performance of the steel seamless gas cylinder has important significance in promoting the technical innovation of related industries, ensuring the safety of personnel and promoting the efficient utilization of energy. As a filling tool, the gas cylinder only reduces the self weight and improves the gas loading capacity of a single gas cylinder, so that the loss in the transportation and carrying processes can be reduced, and the resources are saved. Therefore, in order to achieve a lightweight design of the gas cylinder and to ensure the safety of its use, the gas cylinder steel must have both high strength and high toughness.

At present, cr-Mo alloy steels such as 30CrMo and 35CrMo are mainly adopted as the steel for the seamless gas cylinder, and after quenching and tempering, the tensile strength is less than 1000MPa, and the working pressure is limited to about 20 MPa. However, with increasing demands of high-pressure gas cylinders, especially in application scenarios where working pressure exceeds 35MPa and tensile strength requirements reach over 1100MPa, the strength and toughness of conventional cr—mo steels cannot meet higher requirements. In the steel strengthening method, technical approaches such as precipitation strengthening, grain boundary strengthening and phase transformation strengthening have been widely studied. Wherein, by controlling the addition of alloy elements, refining the grain size, improving the dislocation density and stabilizing the residual austenite structure, the comprehensive performance of the material can be effectively improved. For example, the addition of microalloy elements such as Nb, V and the like can promote the precipitation of fine carbides, generate a strong pinning effect on the material, and remarkably increase the strength without remarkably damaging the toughness. The addition of Ni element can reduce the ductile-brittle transition temperature and improve the low-temperature toughness. As CN102409242A, the mechanical property of the obtained steel for the seamless gas cylinder is improved by adding Ti and Nb microalloy elements. CN115074603A is added with a small amount of Mo and Ni elements, and the strength of the steel is improved by matching with the preparation method. Similarly, the strength improvement of most traditional CrMo steel mainly depends on various carbides formed in the high-temperature tempering process, the toughness improvement mainly depends on the refinement of grain size, the strength improvement is limited and is generally less than 1300 MPa, and the addition of alloy elements greatly increases the production cost.

Meanwhile, in the aspect of heat treatment technology, although the traditional thermal refining can improve the comprehensive performance of materials, the application of the material in the mass production of seamless gas cylinder steel is limited due to complex technology, high energy consumption and severe requirements on equipment in the quenching process. The new generation of heat treatment technology, such as quenching-partitioning (Quenching and Partitioning, Q & P) technology, becomes an effective means for improving the toughness of the steel for the seamless gas cylinder. The core of the Q & P process is that C element is diffused from supersaturated martensite to residual austenite by controlling tempering temperature and tempering time after quenching, so that stable and dispersed residual austenite is formed, further, the plasticity and toughness are improved, and meanwhile, high strength is maintained. IN202111045218 (A) adopts low-carbon alloy components, quenching and non-isothermal partitioning processes, develops a hot rolled steel with a multiphase microstructure containing martensite, bainite, residual austenite and carbide, and has improved mechanical properties to a certain extent. CN 105441814A obtains a three-phase structure of proeutectoid ferrite, martensite and residual austenite containing a certain volume fraction by adopting a sectional cooling process, and also obtains a steel product with superior mechanical properties.

In summary, the Q & P heat treatment process stabilizes a small amount of residual austenite structure to room temperature, so that the ductility and toughness can be effectively improved, but the research on the ductility and toughness, especially the low-temperature transverse impact toughness, of the Q & P steel is less at present due to more attention. However, in the case of seamless gas cylinder steels, due to their special manufacturing process, controlled rolling and cooling techniques cannot be used in the hot rolling process, which presents challenges for the application of Q & P steels. In addition, the Q & P steel is improved in strength and ductility product, meanwhile, the improvement of low-temperature transverse impact toughness is often neglected, and particularly for a gas cylinder needing to operate in an extremely low-temperature environment, the low-temperature toughness of the material is an important factor for determining the safety and reliability of the gas cylinder.

Based on the above, how to cooperatively design steel components and a preparation process, thereby developing and obtaining the low-carbon steel for the seamless gas cylinder with high strength and low temperature high toughness, and becoming a research hot spot in the current material science and engineering fields.

Disclosure of Invention

The invention mainly aims to provide low-carbon steel for a seamless gas cylinder, a preparation method and application thereof, and aims to solve the problem that gas cylinder steel in the prior art is difficult to have high strength and high low-temperature impact toughness.

In order to achieve the aim, the first aspect of the invention provides a preparation method of low-carbon steel for a seamless gas cylinder, which comprises the steps of S1, preparing raw materials according to the components of the low-carbon steel for the seamless gas cylinder, smelting the raw materials according to the weight percentage to obtain a first steel billet, heating the first steel billet to obtain a second steel billet, performing hot rolling at least in the conditions of a starting temperature of 1120-1180 ℃ and a finishing temperature of 880-980 ℃ to obtain a third steel billet, performing hot rolling at least in the steps of S3, performing hot rolling at least in the conditions of a starting temperature of 1120-1180 ℃ and a finishing temperature of 880 ℃, performing hot rolling at least in the steps of S8, and obtaining a seamless steel billet, wherein the raw materials comprise 0.2-0.3 wt% of C, 1.0.0.8-1.8 wt% of Mn, 0.02-0.05 wt% of Ni, and the balance Fe and unavoidable impurity elements.

Further, in the step S2, the heat preservation temperature of the heating treatment is 1200+/-50 ℃ and the heat preservation time is 2-2.5 h.

Further, in the step S3, the start rolling temperature is 1140-1160 ℃ and the finish rolling temperature is 900-960 ℃.

Further, in step S3, the reduction of each hot rolling is less than or equal to 30%.

Further, in the step S4, the metallographic structure of the third steel billet includes a lath martensite phase and a residual austenite phase, and the volume fraction of the area of the residual austenite phase in the metallographic structure is 11.5% -12.5%.

Further, in the step S5, the heat preservation temperature of the heat treatment is 200-350 ℃ and the heat preservation time is 0.5-2.0 h.

The second aspect of the invention provides a low-carbon steel for a seamless gas cylinder, which is prepared by the preparation method of the low-carbon steel for the seamless gas cylinder.

Further, the metallographic structure of the low-carbon steel for the seamless gas cylinder comprises a lath martensite matrix phase and an austenite second phase, and the volume fraction of the area of the austenite second phase in the metallographic structure is 10% -15%.

Further, the yield strength of the low-carbon steel for the seamless gas cylinder is 1300-1400 MPa, and/or the tensile strength of the low-carbon steel for the seamless gas cylinder is 1500-160 MPa, and/or the elongation after fracture of the low-carbon steel for the seamless gas cylinder is 8.0% -14.0%, and/or the transverse impact toughness of the low-carbon steel for the seamless gas cylinder is 40J cm ^-2~70J·cm^-2 at 25+/-2 ℃, and/or the transverse impact toughness of the low-carbon steel for the seamless gas cylinder is 35J cm ^-2~55J·cm^-2 at-50+/-2 ℃.

The third aspect of the invention provides an application of the low-carbon steel for the seamless gas cylinder as a metal material for the seamless gas cylinder in the energy field, the industrial field, the medical field and the aerospace field.

By applying the technical scheme of the invention, the alloy element components of the low-carbon steel for the seamless gas cylinder are carefully designed, and the preparation process is cooperated. Wherein the control of the low carbon content ensures that the obtained low carbon steel can retain a proper amount of retained austenite, and the addition of a plurality of elements with a specific content further refines the microstructure. The combination of the multi-pass hot rolling and tempering heat treatment components not only optimizes the comprehensive mechanical properties of the obtained low-carbon steel, but also ensures that the low-carbon steel shows excellent impact toughness under the low-temperature condition, and finally realizes the comprehensive improvement of the low-temperature toughness and strength of the low-carbon steel for the seamless gas cylinder.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:

FIG. 1 is a time-temperature diagram of the preparation method used in example 1 of the present invention;

FIG. 2 is a graph showing the engineering stress-strain curve of the low carbon steel for the seamless gas cylinder according to the embodiment 1 of the present invention;

FIG. 3 shows the results of the metallographic structure characterization of the low-carbon steel for the seamless gas cylinder obtained in example 1 of the present invention, wherein FIG. 3 (a) is a metallographic photograph obtained by an Optical Microscope (OM), and FIG. 3 (b) is a metallographic structure distribution diagram obtained by Electron Back Scattering Diffraction (EBSD).

Detailed Description

It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other. The present application will be described in detail with reference to examples.

As described in the background art, the prior art gas cylinder steel has a problem that it is difficult to have both high strength and high low temperature impact toughness. In order to solve the technical problems, the first aspect of the invention provides a preparation method of low-carbon steel for a seamless gas cylinder, which comprises the steps of S1, preparing raw materials according to the components of the low-carbon steel for the seamless gas cylinder, S2, heating the raw materials to obtain a first steel billet, heating the first steel billet to obtain a second steel billet, heating the second steel billet at a starting temperature of 1120-1180 ℃ and a finishing temperature of 880 ℃, S3, performing hot rolling to obtain a third steel billet under the conditions of a rolling temperature of 1120-1180 ℃ and a rolling temperature of 880 ℃, S4, cooling the second steel billet to obtain a seamless steel billet, and cooling the third steel billet.

According to the invention, through careful design of alloy element components and cooperation of a preparation process, the comprehensive improvement of low-temperature toughness and strength of the low-carbon steel for the seamless gas cylinder is realized. Aiming at the alloy component elements, the C content is reduced on the basis of the traditional Cr-Mo gas cylinder steel, the toughness loss caused by overhigh C content is reduced, the Mn content is increased to reduce the Ms point, so that stable residual austenite structure can be obtained at room temperature, the plasticity and toughness of the material are improved, a small amount of Nb and V microalloy elements are added, the strength of the steel is obviously improved by separating out nano carbide, and a proper amount of Ni element is added, so that the low-temperature impact toughness of the seamless gas cylinder steel is effectively improved. More specifically:

In the low-carbon steel for the seamless gas cylinder, carbon is the main element for ensuring the strength, the carbon content is too low to meet the strength requirement, but excessive carbon easily generates a brittle phase to damage the toughness of the steel. Based on the content, the content of C is controlled to be preferably 0.2-0.3 wt%.

Si, in the low-carbon steel for the seamless gas cylinder prepared by the invention, silicon plays a solid solution strengthening role in the steel, so that the strength of the steel is improved, and in addition, the silicon element can effectively prevent the production of cementite, so that C can be distributed from martensite to non-transformed austenite in the low-temperature tempering process, and the stability of the austenite is improved. Based on the above, the Si content is controlled to be 1.0wt% to 1.8 wt%.

Mn in the low-carbon steel for the seamless gas cylinder prepared by the invention is the most effective element for improving the strength and the toughness, and is also one of important alloy elements adopted by the invention. Manganese belongs to a typical austenite stabilizing element, can obviously delay pearlite and bainite transformation, and reduces the critical cooling rate of martensite formation, thereby obviously improving the hardenability of steel. In addition, manganese combines with sulfur in the steel to form MnS to prevent hot embrittlement of the steel, so smelting is required to ensure a low S content. However, a high Mn content delays ferrite precipitation and segregation occurs in the center of the steel while delaying pearlite transformation. Based on the above, the Mn content is controlled to be preferably 2.5-4.0 wt%.

Mo in the low carbon steel for seamless gas cylinder, the Mo may be dissolved into ferrite to strengthen the solution. In addition, molybdenum is also a strong carbide forming element, carbide is precipitated in the tempering process, grains are refined, meanwhile, the growth of carbide such as Nb, V and the like can be prevented, the precipitated phase is refined, and the tempering stability is promoted. Based on the above, the content of Mo is controlled to be preferably 0.32-0.50 wt%.

Ni in the low-carbon steel for the seamless gas cylinder, which is prepared by the invention, can strengthen ferrite, reduce ductile-brittle transition temperature, simultaneously can effectively reduce dislocation movement resistance, and can improve low-temperature toughness while enhancing the strength of the steel. Based on the above, the Ni content is controlled to be 0.5wt% to 1.0 wt%.

V in the low-carbon steel for the seamless gas cylinder, vanadium is a strong carbide forming element, and is precipitated to form carbonitride in the tempering process, so that the precipitation strengthening effect is achieved. In addition, the VC particle dissolution temperature is higher, the grain boundary movement can be effectively prevented, the grain refinement effect is good, and the low-temperature impact toughness can be damaged by excessive V. Based on the above, the V content is controlled to be 0.1-0.3 wt%.

Nb in the low carbon steel for the seamless gas cylinder prepared by the invention, niobium is precipitated to form carbonitride in the hot rolling process, fine Nb (C, N) particles are pinned to austenite grain boundaries, the movement of the grain boundaries is prevented, and the dynamic recrystallization of the steel is inhibited. If dynamic recrystallization occurs in the deformation process, the initiated grain boundary migration can enclose microcracks formed at the original grain boundary in new grains, prevent the aggregation, growth and extension of the cracks, and improve the ductility of steel. Based on the above, the Nb content is controlled to be 0.02-0.05 wt%.

Further, there is a synergistic effect between the above-mentioned content ranges of the elemental components. Firstly, the C-Si synergistic effect is that the combination of low carbon content and Si can prevent the formation of brittle phases, meanwhile, si prevents carbide from precipitating, and the stability of residual austenite is maintained, which is important for improving low-temperature toughness. Mn-Ni coupling, wherein the cooperation of Mn and Ni can obviously reduce the martensite transformation temperature, the addition of Ni reduces the ductile-brittle transformation temperature, and the toughness of the material at low temperature is improved under the combined action of the Mn and Ni. Under the synergistic action of Mo, V and Nb, the Mo-V-Nb ternary element not only refines crystal grains and inhibits the movement of crystal boundaries, but also further enhances the low-temperature toughness of the material by separating out fine carbide and carbonitride. That is, the elements in the composition formula of the low-carbon steel for the seamless gas cylinder provided by the invention do not act independently, but act synergistically between each other or between a plurality of elements to form a complete alloy integral formula, and the properties of the low-carbon alloy steel are comprehensively optimized.

On the basis of carrying out fine control on the content of each element, the preparation method is cooperatively optimized. In the actual production and preparation process, the smelting is vacuum smelting, so that the contents of hydrogen and nitrogen in steel are effectively reduced, the effects of hydrogen embrittlement and nitrogen embrittlement are reduced, and the low-temperature toughness is improved. On the basis, the obtained first billet is subjected to heat treatment, so that alloy elements are fully dissolved and homogenized, and a foundation is laid for forming stable microstructure in the subsequent hot rolling and heat treatment processes. In the step S3, the initial rolling temperature is 1120-1180 ℃, the final rolling temperature is 880-980 ℃, and the hot rolling process of at least 8 passes not only promotes the refinement of microstructure, but also maintains a certain amount of austenite phase through the control of the final rolling temperature, and provides favorable conditions for the stable distribution of the residual austenite in the subsequent low-temperature heat treatment, thereby effectively improving the low-temperature toughness of the material. And the subsequent heat treatment, namely, in the low-temperature tempering distribution process, the C element diffuses from martensite to residual austenite, and the formed stable residual austenite can absorb the energy of crack propagation at low temperature, so that the low-temperature fracture toughness of the material is remarkably improved.

In addition, it is worth mentioning that the preparation method directly carries out low-temperature tempering distribution after hot rolling, and the traditional seamless gas cylinder steel needs tempering (quenching and tempering) heat treatment process. Therefore, compared with the prior art, the preparation method provided by the invention can obtain the low-carbon steel with excellent comprehensive performance by matching alloy components with the process route, thereby simplifying the heat treatment process route, reducing the energy consumption caused by processing, saving resources and particularly conforming to the development concept of a resource-saving society.

In the preparation method, for the heating treatment in the step S2, in order to enable the alloy elements to be more fully dissolved and distributed, so as to facilitate the improvement of the structural uniformity of the obtained first billet in the subsequent treatment process and finally improve the performances of the obtained low carbon steel for the seamless steel cylinder, the heat preservation temperature is preferably 1200+/-50 ℃ and the heat preservation time is preferably 2-2.5 h.

In the multi-pass hot rolling in the step S3, it is further preferable that the start rolling temperature is 1140 ℃ to 1160 ℃ and the finish rolling temperature is 900 ℃ to 960 ℃. The initial rolling temperature of 1140-1160 ℃ can better ensure the sufficient formation of austenite, and the narrower final rolling temperature range of 900-960 ℃ ensures that the structure transformation of the billet in the cooling process is controllable, thereby more remarkably promoting the formation of stable residual austenite and more effectively enhancing the low-temperature toughness of the finally obtained low-carbon steel.

On the basis, in the step S3, the reduction of each hot rolling is more preferably less than or equal to 30 percent, so that the deformation in the hot rolling process is more effectively controlled, internal cracks or structural defects caused by excessive deformation are reduced, fine grains are further promoted, and the plasticity and toughness of the obtained low-carbon steel, particularly the impact toughness at low temperature, are improved. Through a large number of experiments, in several typical embodiments, the pass of hot rolling is definitely preferably 8, so that more sufficient plastic deformation can be realized under the conditions of more remarkably simplifying the process, reducing the energy consumption and not damaging the internal structure of the material, and the microstructure of the steel billet is more effectively thinned, so that the overall plastic toughness of the material, particularly the transverse impact toughness at low temperature, is more effectively improved. In practical application, in order to better control the deformation degree in the hot rolling process and the cooling speed of the steel billet, obtain a more uniform metallographic structure and obtain more excellent toughness and plasticity, the thickness of the first steel billet is preferably 80+/-5 mm, and the thickness of the second steel billet is preferably 6-7.5 mm.

Based on the optimization of the above process condition parameters, in step S4, it is preferable that the metallographic structure of the obtained third billet includes lath martensite phase and residual austenite phase, and the volume fraction of the area of the residual austenite phase in the metallographic structure is 11.5% -12.5%. The volume fraction of the residual austenite in the metallographic structure of the intermediate product, namely the third billet, is preferably higher than that of the intermediate product, so that the billet can be better promoted to respond more sensitively in the subsequent heat treatment (low-temperature tempering distribution), and further the effective diffusion of the C element and the stable retention of the residual austenite are more obviously promoted, so that the finally obtained low-carbon steel can maintain high strength and simultaneously improve the low-temperature toughness more obviously, and the performance requirement of the steel for a seamless gas cylinder in an extreme environment is better met.

In several exemplary embodiments, in step S5, the heat treatment is performed at a temperature of 200 ℃ to 350 ℃ for a time of 0.5h to 2.0h. In the low-temperature tempering stage of 200-350 ℃, C element can be more efficiently diffused into residual austenite from supersaturated martensite to form a more stable and dispersed residual austenite structure, and the heat preservation time of 0.5-2.0 h promotes the diffusion process to be more fully carried out, so that the stability of the residual austenite phase is further promoted, the residual austenite phase can still act as a toughness phase at a low temperature, and finally the low-temperature toughness of the obtained low-carbon steel is more remarkably improved. And the cooling mode of the heat treatment is preferably air cooling, so that the retained austenite phase is more stably stored, the supersaturation degree of the martensite phase possibly caused by rapid cooling (such as water cooling) is reduced, the embrittlement risk is further reduced, the integrity of the surface of the low-carbon steel for the obtained seamless steel cylinder is improved, the generation of cracks is reduced, and the surface quality and the subsequent use safety are optimized.

The second aspect of the invention provides a low-carbon steel for a seamless gas cylinder, which is prepared by the preparation method of the low-carbon steel for the seamless gas cylinder. Through the synergistic effect of the manufacturing process and the component design, the low-carbon steel for the seamless gas cylinder, which has high strength and excellent low-temperature toughness, is prepared, so that the requirements of the seamless gas cylinder on light weight and high safety can be well met.

Further, the metallographic structure of the prepared low-carbon steel for the seamless gas cylinder comprises a lath martensite matrix phase and an austenite second phase, and the volume fraction of the area of the austenite second phase in the metallographic structure is 10% -15%, preferably 11.5% -12.0%. In the above preferred and more preferred volume fraction ranges, the retained austenite phase in the resulting low carbon steel metallographic structure can be more uniformly distributed so as to further reduce crack initiation and propagation, and more significantly improve the fracture toughness of the resulting low carbon steel at low temperatures.

In several preferred embodiments, the yield strength of the low carbon steel for the seamless gas cylinder is 1300-1400 MPa, and/or the tensile strength of the low carbon steel for the seamless gas cylinder is 1500-160 MPa, and/or the elongation after fracture of the low carbon steel for the seamless gas cylinder is 8.0% -14.0%, and/or the transverse impact toughness of the low carbon steel for the seamless gas cylinder is 40J cm ^-2~70J·cm^-2 at 25+ -2 ℃, and/or the transverse impact toughness of the low carbon steel for the seamless gas cylinder is 35J cm ^-2~55J·cm^-2 at-50+ -2 ℃. That is, the low carbon steel for a seamless gas cylinder prepared by the preparation method has excellent mechanical properties including yield strength, tensile strength and elongation after fracture, and also exhibits excellent transverse impact toughness at room temperature, especially at low temperature, and can provide more remarkable safety and reliability for various metal products when being prepared.

The third aspect of the invention provides an application of the low-carbon steel for the seamless gas cylinder as a metal material for the seamless gas cylinder in the energy field, the industrial field, the medical field and the aerospace field. The low-carbon steel obtained by the invention has high strength, high fracture toughness, low ductile-brittle transition temperature and good ductility which can be maintained at low temperature, so that the low-carbon steel can be used as a metal material for a seamless gas cylinder to remarkably improve the reliability and safety of the obtained seamless gas cylinder product, thereby being capable of meeting the application requirements in various fields such as energy fields, industrial fields, medical fields, aerospace fields and the like.

The application is described in further detail below in connection with specific examples which are not to be construed as limiting the scope of the application as claimed.

Unless defined otherwise, all technical and scientific terms used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the scope of the present invention.

Example 1

The preparation method of the low-carbon steel for the seamless gas cylinder comprises the following steps:

(1) The raw materials were formulated according to the composition of the low carbon steel for seamless gas cylinders to be produced, comprising 0.25wt% of C, 1.5wt% of Si, 3.0wt% of Mn, 0.4wt% of Mo, 0.8wt% of Ni, 0.13wt% of V, 0.04wt% of Nb, and the balance of Fe and unavoidable impurity elements (the composition is as shown in Table 1);

(2) Smelting the chemical components to obtain a target billet of 80 multiplied by 80 mm, namely a first billet, feeding the obtained billet sample into a heating furnace, heating to the complete austenitizing temperature of 1200 ℃, and preserving heat for 2h to obtain a second billet;

(3) Carrying out 8-pass hot rolling on the billet sample after being discharged from the furnace, carrying out initial rolling at 1160 ℃, and carrying out 8-pass hot rolling on the billet from 80 mm to 7 mm, wherein the single-pass pressing quantity is respectively 30% -30% -30% -25% -25% -20% -20%, and the final rolling temperature is 950 ℃;

(4) Cooling the sample in the step (3) to room temperature by air to obtain a third billet, wherein the metallographic structure of the third billet comprises a lath martensite phase and a residual austenite phase;

(5) And (3) placing the sample obtained in the step (4) in an arc furnace with the temperature of 200 ℃, tempering and preserving heat of 1 h, and air-cooling to room temperature to obtain the low-carbon steel for the seamless gas cylinder.

And, the time-temperature process diagram of the preparation method is shown in fig. 1.

Example 2

(1) The raw materials were formulated according to the composition of the low carbon steel for seamless gas cylinders to be produced, comprising 0.27wt% of C, 1.2wt% of Si, 3.3wt% of Mn, 0.32wt% of Mo, 1.0wt% of Ni, 0.15wt% of V, 0.03wt% of Nb, and the balance of Fe and unavoidable impurity elements (the composition is as shown in Table 1);

(3) Carrying out 8-pass hot rolling on the billet sample after being discharged from the furnace, starting rolling at 1170 ℃, and carrying out 8-pass hot rolling on the billet from 80 mm to 6.5 mm, wherein the single-pass reduction is the same as that of example 1, and the final rolling temperature is 960 ℃;

(5) And (3) placing the sample obtained in the step (4) in an arc furnace with the temperature of 300 ℃, tempering and preserving heat of 2h, and air-cooling to room temperature to obtain the low-carbon steel for the seamless gas cylinder.

Example 3

(1) The raw materials were formulated according to the composition of the low carbon steel for seamless gas cylinders to be produced, comprising 0.23wt% of C, 1.0wt% of Si, 3.8wt% of Mn, 0.43wt% of Mo, 0.65wt% of Ni, 0.12wt% of V, 0.02wt% of Nb, and the balance of Fe and unavoidable impurity elements (the composition is as shown in Table 1);

(3) Carrying out 8-pass hot rolling on the billet sample after being discharged from the furnace, carrying out initial rolling at 1160 ℃, and carrying out 8-pass hot rolling on the billet from 80 mm to 6.5 mm, wherein the single-pass reduction is the same as that of example 1, and the final rolling temperature is 950 ℃;

(5) And (3) placing the sample obtained in the step (4) in an arc furnace with the temperature of 350 ℃, tempering and preserving heat by 0.5h, and air-cooling to room temperature to obtain the low-carbon steel for the seamless gas cylinder.

Example 4

This example differs from example 1 only in that in step (2), the holding temperature was changed to 1100 ℃ and the holding time was changed to 5 hours.

Example 5

this example differs from example 1 only in that in step (3), the start rolling temperature is changed to 1120 ℃ and the finish rolling temperature is changed to 880 ℃.

Example 6

this example differs from example 1 only in that in step (3), the start rolling temperature is changed to 1180 ℃ and the finish rolling temperature is changed to 980 ℃.

Example 7

This example differs from example 1 only in that in step (3), the thickness of the slab before hot rolling was changed to 100mm, and 8 passes of hot rolling were performed to obtain a hot rolled slab having a thickness of 5mm, in which the single pass reduction amounts were 35% -35% -30% -30% -30% -30%, respectively.

Example 8

this example differs from example 1 only in that in step (5), the holding temperature was changed to 150 ℃ and the holding time was changed to 3 hours.

Example 9

this example differs from example 1 only in that in step (5), the holding temperature was changed to 400℃and the holding time was changed to 20 minutes.

Comparative example 1 and comparative example 2

Comparative example 1 and comparative example 2 differ from example 1 only in the content of the elements, and are shown in Table 1.

Comparative example 3

A preparation method of steel for a seamless gas cylinder comprises the following steps:

This comparative example differs from example 1 only in that in step (3), the start rolling temperature was changed to 1100 ℃ and the finish rolling temperature was changed to 800 ℃.

Comparative example 4

This comparative example differs from example 1 only in that in step (3), the start rolling temperature was changed to 1200 ℃ and the finish rolling temperature was changed to 1000 ℃.

Comparative example 5

this comparative example differs from example 1 only in that in step (3), the hot rolling pass was changed to 5 and the billet was rolled from 80 mm to 7.5 mm, wherein the single pass reduction was 40% -40% -35% -35% -35%, respectively.

Test method

Yield strength was measured according to GB/T221.1-2021.

Tensile strength is measured according to GB/T221.1-2021.

The elongation after break was tested according to GB/T221.1-2021.

Transverse impact toughness was measured according to GB/T229-2020 and obtained for the steel samples at room temperature (25.+ -. 2 ℃ C.) and at-50 ℃ C., respectively.

The metallographic structure and the phase distribution diagram are tested according to GB/T38420-2020 and GB/T34720-2017 respectively, and the volume ratio of the residual austenite phase in the metallographic structure of the third billet in each example and comparative example and the volume ratio of the residual austenite phase in the metallographic structure of the finally obtained low-carbon steel for the seamless gas cylinder are obtained respectively.

The above test was performed on each of the examples and the comparative examples and comparative examples, and the results obtained are shown in table 2. And the engineering stress-strain curve of the obtained example 1 is shown in fig. 2, the metallographic photograph of the low-carbon steel for the seamless gas cylinder obtained in the example 1 is shown in fig. 3 (a), and the metallographic structure diagram is shown in fig. 3 (b).

TABLE 1

TABLE 2

From the above description, it can be seen that the above examples of the present invention realize the production of low carbon steel for seamless steel cylinders superior in combination properties as compared with the respective comparative examples. The obtained low-carbon steel has excellent mechanical properties including yield strength, tensile strength and elongation after fracture, and also has excellent transverse impact toughness at room temperature, especially at low temperature, and can provide more remarkable safety and reliability for various metal products when being prepared.

As is clear from comparative examples 1 and 2, the absence of synergistic control and adjustment of the elements in the low carbon steel resulted in a significant decrease in the strength and plasticity of comparative example 1, while comparative example 2 exhibited a higher strength but poor plasticity and also had poor impact toughness at normal and low temperatures.

As is clear from comparative examples 3 to 5, in step S3, the hot rolling process of at least 8 passes, in which the start rolling temperature is 1120 ℃ to 1180 ℃ and the finish rolling temperature is 880 ℃ to 980 ℃, is strictly controlled, not only promotes the refinement of microstructure, but also retains a certain amount of austenite phase by the finish rolling temperature control, and provides favorable conditions for the stable distribution of the retained austenite in the subsequent low-temperature heat treatment, thereby effectively improving the low-temperature toughness of the material.

In each example, comparing example 4 with example 1, it is evident that the heat treatment is preferable in step (2) to enable the alloying elements to be more fully dissolved and distributed so as to promote the structural uniformity of the obtained first billet during the subsequent treatment, and finally promote the properties of the obtained low carbon steel for the seamless steel cylinder, in particular, the low temperature impact toughness.

Comparing examples 5 and 6 with example 1, it is known that by further optimizing the start rolling temperature and the finish rolling temperature in step (3), sufficient formation of austenite can be better ensured, and meanwhile, the transformation of the structure of the billet in the cooling process is promoted to be controllable, so that the formation of stable residual austenite is more remarkably promoted, the volume fraction of the area of the residual austenite phase in the metallographic structure is optimized, and finally, the low-temperature toughness of the finally obtained low-carbon steel is more effectively enhanced.

Comparing example 7 with example 1, it is found that by further optimizing the rolling pass in step (3) and the reduction per pass, it is possible to achieve more sufficient plastic deformation under the conditions of more significantly simplifying the process, reducing the energy consumption, and not damaging the internal structure of the material, and also to refine the microstructure of the billet at this time more efficiently, thereby more effectively improving the overall plastic toughness of the material, particularly the transverse impact toughness at low temperatures.

Comparing examples 8 and 9 with example 1, it is evident that by optimizing the heat treatment temperature and time in step (5), the C element can be promoted to diffuse from supersaturated martensite into retained austenite more efficiently, forming a more stable and diffuse retained austenite structure, thereby further promoting the stability of the retained austenite phase, allowing it to still function as a ductile phase at low temperature, and eventually further significantly improving the low temperature toughness of the resulting low carbon steel.

It should be noted that the terms "first," "second," and the like in the description and in the claims are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those described herein.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing low-carbon steel for a seamless gas cylinder, which is characterized by comprising the following steps:

The method comprises the following steps of S1, preparing raw materials according to the components of the low-carbon steel for the seamless gas cylinder, wherein the components of the low-carbon steel for the seamless gas cylinder comprise, by weight, 0.2-0.3% of C, 1.0-1.8% of Si, 2.5-4.0% of Mn, 0.32-0.50% of Mo, 0.5-1.0% of Ni, 0.1-0.3% of V, 0.02-0.05% of Nb, and the balance of Fe and unavoidable impurity elements;

Step S2, smelting the raw materials to obtain a first steel billet, and heating the first steel billet to obtain a second steel billet;

S3, carrying out at least 8 times of hot rolling on the second billet under the condition that the initial rolling temperature is 1120-1180 ℃ and the final rolling temperature is 880-980 ℃ to obtain a hot rolled billet;

s4, performing air cooling on the hot rolled steel billet to obtain a third steel billet;

And S5, carrying out heat treatment on the third steel billet to obtain the low-carbon steel for the seamless gas cylinder, wherein the heat preservation temperature of the heat treatment is 200-350 ℃, the heat preservation time is 0.5-2.0 h, and the cooling mode of the heat treatment is air cooling.

2. The method for producing a low carbon steel for a seamless gas cylinder according to claim 1, wherein in the step S2, the heat-preserving temperature of the heat treatment is 1200±50 ℃ and the heat-preserving time is 2h to 2.5h.

3. The method for producing a low carbon steel for a seamless gas cylinder according to claim 1, wherein in the step S3, the start rolling temperature is 1140 ℃ to 1160 ℃ and the finish rolling temperature is 900 ℃ to 960 ℃.

4. The method for producing a low carbon steel for a seamless gas cylinder according to any one of claims 1 to 3, wherein in the step S3, the reduction of the hot rolling is not more than 30%.

5. The method according to any one of claims 1 to 3, wherein in the step S4, the microstructure of the third billet includes a lath martensite phase and a retained austenite phase, and the area of the retained austenite phase is 11.5% to 12.5% by volume in the microstructure.

6. A low carbon steel for a seamless gas cylinder, characterized in that the low carbon steel for a seamless gas cylinder is produced by the production method of the low carbon steel for a seamless gas cylinder as set forth in any one of claims 1 to 5.

7. The low carbon steel for a seamless gas cylinder according to claim 6, wherein the metallographic structure of the low carbon steel for a seamless gas cylinder comprises a lath martensite matrix phase and an austenite second phase, and the area of the austenite second phase is 10% -15% by volume in the metallographic structure.

8. The low-carbon steel for a seamless gas cylinder according to claim 6 or 7, wherein,

The yield strength of the low-carbon steel for the seamless gas cylinder is 1300-1400 MPa and/or,

The tensile strength of the low-carbon steel for the seamless gas cylinder is 1500-160 MPa, and/or,

The elongation after fracture of the low-carbon steel for the seamless gas cylinder is 8.0% -14.0%, and/or,

The low carbon steel for the seamless gas cylinder has a transverse impact toughness of 40J cm ^-2~70J·cm^-2 at 25+/-2 ℃ and/or,

The transverse impact toughness of the low-carbon steel for the seamless gas cylinder is 35 J.cm ^-2~55J·cm^-2 at the temperature of minus 50+/-2 ℃.

9. Use of the low carbon steel for a seamless gas cylinder according to any one of claims 6 to 8 as a metal material for a seamless gas cylinder in the energy field, the industrial field, the medical field and the aerospace field.