Alloy steel for ultra-high pressure gas cylinder and preparation method therefor

Abstract

The present invention discloses alloy steel for an ultra-high pressure gas cylinder and a preparation method thereof. In chemical compositions of the steel, P+S≤0.012%, and Nb+V+Ti+B+Zr≤0.10%. In the preparation method, the alloy steel for the ultra-high pressure gas cylinder is subjected to heat treatment through normalizing + quenching + tempering, including: normalizing pretreatment, heating to 860±5°C, and cooling outside a furnace to 25°C or below after heat preservation of 60-90 min; quenching treatment, raising a temperature to 860±5°C, and water-cooling to a room temperature after heat preservation of 60-90 min; and high-temperature tempering treatment, heating to 560±5°C, and air-cooling outside a furnace to the room temperature after heat preservation of 120-150 min. In the present invention, yield strength of the alloy steel reaches 980 MPa or above, tensile strength of the alloy steel reaches 1100 MPa or above, and a -50°C low-temperature impact value of the alloy steel reaches 50 J / cm2 or above, which are suitable for manufacturing the ultra-high pressure gas cylinder.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the technical field of alloy steel for gas cylinders, and particularly relates to alloy steel for an ultra-high pressure gas cylinder and a preparation method thereof.BACKGROUND

[0002] Ultra-high pressure gas cylinder with a working pressure of 30 MPa is used for filling of compressed gases such as O 2 , N 2 , Ar, He, H 2 and CNG, its wall thickness is designed to be smaller than that of high-pressure gas cylinder made of general materials, so that the lightweight of the high-pressure gas cylinder is achieved, resources are saved, transportation losses are reduced, a gas loading capacity of a single high-pressure gas cylinder is greatly increased, favorable conditions are provided for the use of gases, and broad use in the fields such as industry, civil use and national defense is achieved.

[0003] In the prior art, the gas cylinders are usually manufactured from 34CrMo4 alloy steel, but the 34CrMo4 alloy steel is only suitable for a common gas cylinder with a working pressure of 15 MPa, and because the material strength is low, the low-temperature impact performance is insufficient, and the service life is short, it is difficult to use in manufacturing of ultra-high pressure gas cylinders.SUMMARY

[0004] In order to solve the above technical problems in the prior art, the present invention provides an alloy steel for an ultra-high pressure gas cylinder and a preparation method thereof. By designing compositions of the alloy steel and optimizing a heat treatment process, the strength and impact performance of the alloy steel are improved, and thus the alloy steel is suitable for manufacturing and use of the ultra-high pressure gas cylinder.

[0005] In an aspect of the present invention, alloy steel for an ultra-high pressure gas cylinder is provided. Chemical compositions of the alloy steel for the ultra-high pressure gas cylinder are controlled to be, by mass percentage: C: 0.32-0.36%, Si: 0.15-0.30%, Mn: 0.60-0.80%, Cr: 0.95-1.15%, Mo: 0.20-0.30%, A1: 0.02-0.04%, Nb: 0.015-0.025%, Ti: 0.015-0.025%, P≤0.007%, S≤0.005%, Ni: 0.12-0.20%, Cu≤0.10%, Sn≤0.005%, As≤0.005%, H≤0.00015%, N≤0.007%, O≤0.002%, the balance Fe and inevitable impurities, wherein P+S≤0.012% and Nb+V+Ti+B+Zr≤0.10%.

[0006] Further, in the above alloy steel for the ultra-high pressure gas cylinder, the chemical compositions of the alloy steel for the ultra-high pressure gas cylinder are, by mass percentage: C: 0.33%, Si: 0.22%, Mn: 0.70%, P: 0.005%, S: 0.001%, Cr: 1.03%, Mo: 0.26%, A1: 0.026%, Nb: 0.025%, Ti: 0.020%, Ni: 0.18%, Cu: 0.01%, B: 0.0005%, H: 0.000058%, N: 0.0056%, O: 0.0012%, the balance Fe and inevitable impurities.

[0007] Further, in the above alloy steel for the ultra-high pressure gas cylinder, yield strength of the alloy steel for the ultra-high pressure gas cylinder is 980 MPa or above, tensile strength of the alloy steel for the ultra-high pressure gas cylinder is 1100 MPa or above, and a -50°C low-temperature impact value of the alloy steel for the ultra-high pressure gas cylinder is 50 J / cm 2< or above.

[0008] In another aspect of the present invention, a preparation method of alloy steel for an ultra-high pressure gas cylinder is provided, including: performing smelting, die casting and rolling to obtain an alloy steel plate for the ultra-high pressure gas cylinder, wherein during smelting, chemical compositions of the steel are controlled to be, by mass percentage: C: 0.32-0.36%, Si: 0.15-0.30%, Mn: 0.60-0.80%, Cr: 0.95-1.15%, Mo: 0.20-0.30%, A1: 0.02-0.04%, Nb: 0.015-0.025%, Ti: 0.015-0.025%, P≤0.007%, S≤0.005%, Ni: 0.12-0.20%, Cu≤0.10%, Sn≤0.005%, As≤0.005%, H≤0.00015%, N≤0.007%, O≤0.002%, the balance Fe and inevitable impurities, wherein P+S≤0.012% and Nb+V+Ti+B+Zr≤0.10%; and performing heat treatment to the alloy steel plate for the ultra-high pressure gas cylinder, wherein the heat treatment is performed through normalizing + quenching + tempering, and includes the following specific processes: normalizing pretreatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in a high-temperature furnace and heated to 860±5°C, and after heat preservation time of 60-90 min, the alloy steel plate is naturally cooled to 25°C or below in air outside the furnace, or the alloy steel plate is subjected to accelerated cooling to 25°C or below through water-mist cooling or cold-air-blowing forced air cooling outside the furnace; quenching treatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in the high-temperature furnace and heated to 860±5°C at a heating speed of 3-5°C / min, and after heat preservation time of 60-90 min, the alloy steel plate is soaked in water to be cooled to a room temperature; and high-temperature tempering treatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in a tempering furnace and heated to 560±5°C, and after heat preservation time of 120-150 min, the alloy steel plate is cooled to the room temperature in air outside the furnace.

[0009] Further, in the above preparation method of the alloy steel for the ultra-high pressure gas cylinder, the alloy steel for the ultra-high pressure gas cylinder is smelted using 80-ton electric furnace smelting + LF furnace refining + a VD process, wherein the alloy steel has chemical compositions, by mass percentage: C: 0.33%, Si: 0.22%, Mn: 0.70%, P: 0.005%, S: 0.001%, Cr: 1.03%, Mo: 0.26%, A1: 0.026%, Nb: 0.025%, Ti: 0.020%, Ni: 0.18%, Cu: 0.01%, B: 0.0005%, H: 0.000058%, N: 0.0056%, O: 0.0012%, the balance Fe and inevitable impurities; the alloy steel for the ultra-high pressure gas cylinder is die-cast into a blank, and then the blank is rolled to obtain the alloy steel plate for the ultra-high pressure gas cylinder with a thickness of 20 mm; the alloy steel plate for the ultra-high pressure gas cylinder is subjected to heat treatment, including the following specific processes: normalizing pretreatment, the alloy steel plate for the ultra-high pressure gas cylinder is placed in the high-temperature furnace and heated to 860°C, and after heat preservation of 60 min, the alloy steel plate is naturally cooled to a room temperature of 23°C in air outside the furnace; quenching treatment, the alloy steel plate for the ultra-high pressure gas cylinder is placed in the high-temperature furnace and heated to 860°C at a heating speed of 3-5°C / min, and after heat preservation of 60 min, the steel plate is soaked in water to be cooled to a room temperature; and high-temperature tempering treatment, the alloy steel plate for the ultra-high pressure gas cylinder is placed in the tempering furnace and heated to 560°C, and after heat preservation of 120 min, the alloy steel plate is cooled to the room temperature in air outside the furnace.

[0010] The alloy steel for the ultra-high pressure gas cylinder and the preparation method thereof in the present invention have the following advantages and beneficial effects.

[0011] By designing the compositions of the alloy steel and optimizing the heat treatment process, the yield strength of the steel reaches 980 MPa or above, the tensile strength of the steel reaches 1100 MPa or above, and the -50°C low-temperature impact value of the steel reaches 50 J / cm 2< or above. The yield strength, the tensile strength and the low-temperature impact performance of the alloy steel for the ultra-high pressure gas cylinder are remarkably improved, so that the alloy steel is completely suitable for the manufacturing and use of the ultra-high pressure gas cylinder, and the requirements for high quality, long life and lightweight in the ultra-high pressure gas cylinder industry are met.DESCRIPTION OF EMBODIMENTS

[0012] In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Apparently, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without any creative work will fall within the protection scope of the present invention.

[0013] Alloy compositions in steel determine its physical properties, chemical properties, and processing performance. An appropriate alloy content ratio can make the steel have excellent performance and meet production and application requirements. Therefore, in order to achieve the purposes of improving the strength and impact performance of steel in the present invention, it is necessary to optimize the alloy compositions of steel for gas cylinders. To this end, the inventor designs compositions of alloy steel for an ultra-high pressure gas cylinder, the contents of niobium and titanium in the steel are increased, nitrogen and sulfur and fixed with titanium, the structure of an as-cast matrix is refined, grain refinement is achieved, and the strength of the steel is increased; after normalizing treatment, grains are further refined, when normalizing is performed at an appropriate high temperature, high-melting-point carbides are precipitated, dispersed refinement is conducted, dispersion strengthening is further achieved during cooling, and the plasticity and impact toughness of the steel are remarkably improved; and niobium has a strong inhibitory effect on recrystallization, austenite recrystallization is inhibited through a solute drag effect of carbonitrides of non-solid-dissolved niobium and solid-dissolved niobium, ferrite grains are refined, while another important role of niobium is to achieve a precipitation strengthening effect. After adding niobium and titanium elements, the interaction between the two reduces the activity of their carbonitrides, increases solubility, increases their stability in austenite, reduces precipitation tendency, and lowers a precipitation temperature, and thus precipitated particles are finer. On the whole, both niobium and titanium can improve the strength and toughness of steel. Their combined use with other alloy elements can achieve more comprehensive performance improvement.

[0014] In addition, heat treatment of steel is an operation method of obtaining a desired microstructure and performance by heating the steel in a solid state to a given temperature and preserving the temperature for a period of time, and then cooling the steel at a specific speed and with a specific method. Normalizing is used as prior heat treatment before quenching, steel is heated to a temperature 30-50°C higher than an Ac3 temperature, then air cooling is carried out after heat preservation of a period of time, an overheated coarse grain structure and a Widmanstatten structure of castings can be eliminated, and grains are refined. Quenching is to heat the steel to a temperature higher than Ac3, make the steel austenitized after heat preservation of a period of time, and then rapidly cool the steel to a temperature below Ms at a cooling speed greater than a critical cooling rate for performing martensitic transformation. High-temperature tempering is to heat the steel to 500-650°C again after quenching and cool the steel at an appropriate speed after heat preservation of a period of time, after high-temperature tempering treatment, the morphology of carbides in the material structure is changed from flaky to fine granular, and distribution is changed from uneven to dispersed, so that the impact toughness of the material is improved.

[0015] As an implementation of the present invention, chemical compositions of the alloy steel for an ultra-high pressure gas cylinder of the present invention are controlled to be, by mass percentage: C: 0.32-0.36%, Si: 0.15-0.30%, Mn: 0.60-0.80%, Cr: 0.95-1.15%, Mo: 0.20-0.30%, A1: 0.02-0.04%, Nb: 0.015-0.025%, Ti: 0.015-0.025%, P≤0.007%, S≤0.005%, Ni: 0.12-0.20%, Cu≤0.10%, Sn≤0.005%, As≤0.005%, H≤0.00015%, N≤0.007%, O≤0.002%, the balance Fe and inevitable impurities, wherein P+S≤0.012% and Nb+V+Ti+B+Zr≤0.10%.

[0016] Further, as for the alloy steel for the ultra-high pressure gas cylinder of the present invention, yield strength is 980 MPa or above, tensile strength is 1100 MPa or above, and a -50°C low-temperature impact value is 50 J / cm 2< or above.

[0017] As an implementation of the present invention, a preparation method of alloy steel for an ultra-high pressure gas cylinder of the present invention includes: smelting, die casting and rolling are performed to obtain an alloy steel plate for the ultra-high pressure gas cylinder, wherein during smelting, chemical compositions of the steel are controlled to be, by mass percentage: C: 0.32-0.36%, Si: 0.15-0.30%, Mn: 0.60-0.80%, Cr: 0.95-1.15%, Mo: 0.20-0.30%, A1: 0.02-0.04%, Nb: 0.015-0.025%, Ti: 0.015-0.025%, P≤0.007%, S≤0.005%, Ni: 0.12-0.20%, Cu≤0.10%, Sn≤0.005%, As≤0.005%, H≤0.00015%, N≤0.007%, O≤0.002%, the balance Fe and inevitable impurities, wherein P+S≤0.012% and Nb+V+Ti+B+Zr≤0.10%; and heat treatment is performed to the alloy steel plate for the ultra-high pressure gas cylinder, wherein the heat treatment is performed through normalizing + quenching + tempering, and a specific implementing process includes the following steps: normalizing pretreatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in a high-temperature furnace and heated to 860±5°C, and after heat preservation time of 60-90 min, the alloy steel plate is cooled to 25°C or below outside the furnace; quenching treatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in the high-temperature furnace and heated to 860±5°C at a heating speed of 3-5°C / min, and after heat preservation time of 60-90 min, the steel plate is soaked in water to be cooled to a room temperature; and high-temperature tempering treatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in a tempering furnace and heated to 560±5°C, and after heat preservation time of 120-150 min, the alloy steel plate is cooled to the room temperature in air outside the furnace.

[0018] As a specific implementation, in the preparation method of the alloy steel for the ultra-high pressure gas cylinder of the present invention, after the heat preservation time of normalizing pretreatment is over, the alloy steel may be naturally cooled to 25°C or below in air outside the furnace, or the alloy steel may be subjected to accelerated cooling to 25°C or below through forced air cooling approaches such as water-mist cooling or cold air blowing outside the furnace.

[0019] After being tested, the alloy steel for the ultra-high pressure gas cylinder prepared using the preparation method of the alloy steel for the ultra-high pressure gas cylinder of the present invention has yield strength of 980 MPa or above, tensile strength of 1100 MPa or above, and a -50°C low-temperature impact value of 50 J / cm 2< or above.

[0020] The alloy steel for the ultra-high pressure gas cylinder and the preparation method thereof in the present invention are described in detail below in combination with specific embodiments.

[0021] In an embodiment of the present invention, the alloy steel for the ultra-high pressure gas cylinder is smelted using 80-ton electric furnace smelting +LF furnace refining + a VD process, wherein the alloy steel has chemical compositions, by mass percentage: C: 0.33%, Si: 0.22%, Mn: 0.70%, P: 0.005%, S: 0.001%, Cr: 1.03%, Mo: 0.26%, A1: 0.026%, Nb: 0.025%, Ti: 0.020%, Ni: 0.18%, Cu: 0.01%, B: 0.0005%, H: 0.000058%, N: 0.0056%, O: 0.0012%, the balance Fe and inevitable impurities.

[0022] The above alloy steel for the ultra-high pressure gas cylinder is die-cast into a blank, and then the blank is rolled to obtain an alloy steel plate for the ultra-high pressure gas cylinder with a thickness of 20 mm, and the alloy steel plate for the ultra-high pressure gas cylinder is subjected to heat treatment, which includes a specific process: normalizing pretreatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in a high-temperature furnace and heated to 860°C, and after heat preservation of 60 min, the alloy steel plate is naturally cooled to a room temperature of 23°C in air outside the furnace; quenching treatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in the high-temperature furnace and heated to 860°C at a heating speed of 3-5°C / min, and after heat preservation of 60 min, the steel plate is soaked in water to be cooled to a room temperature; and high-temperature tempering treatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in a tempering furnace and heated to 560°C, and after heat preservation of 120 min, the alloy steel plate is cooled to the room temperature in air outside the furnace.

[0023] After being tested, the alloy steel for the ultra-high pressure gas cylinder prepared using the above embodiment of the present invention has yield strength of 1058 MPa, tensile strength of 1136 MPa, and a -50°C low-temperature impact value of 51 J / cm 2< .

[0024] In conclusion, according to the alloy steel for the ultra-high pressure gas cylinder and the preparation method thereof in the present invention, by designing the compositions of the alloy steel and optimizing the heat treatment process, the yield strength of the alloy steel reaches 980 MPa or above, the tensile strength of the alloy steel reaches 1100 MPa or above, and the -50°C low-temperature impact value of the alloy steel reaches 50 J / cm 2< or above; the yield strength, the tensile strength and the low-temperature impact performance of the alloy steel are remarkably improved, the alloy steel is completely suitable for the manufacturing and use of the ultra-high pressure gas cylinder, and the requirements for high quality, long life and lightweight in the ultra-high pressure gas cylinder industry are met.

[0025] It should be noted that, the above embodiments are only used to illustrate the technical solution of the present invention, not to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those ordinarily skilled in the art shall understand that: they can still modify the technical solution recorded in the aforementioned embodiments or make equivalent replacements for part of the technical features; and these modifications or replacements do not separate the essence of the corresponding technical solution from the scope of the present invention.

Claims

1. An alloy steel for an ultra-high pressure gas cylinder, wherein chemical compositions of the alloy steel for the ultra-high pressure gas cylinder are controlled to be, by mass percentage: C: 0.32-0.36%, Si: 0.15-0.30%, Mn: 0.60-0.80%, Cr: 0.95-1.15%, Mo: 0.20-0.30%, A1: 0.02-0.04%, Nb: 0.015-0.025%, Ti: 0.015-0.025%, P≤0.007%, S≤0.005%, Ni: 0.12-0.20%, Cu≤0.10%, Sn≤0.005%, As≤0.005%, H≤0.00015%, N≤0.007%, O≤0.002%, the balance Fe and inevitable impurities, wherein P+S≤0.012% and Nb+V+Ti+B+Zr≤0.10%.

2. The alloy steel for the ultra-high pressure gas cylinder according to claim 1, wherein the alloy steel for the ultra-high pressure gas cylinder has chemical compositions, by mass percentage: C: 0.33%, Si: 0.22%, Mn: 0.70%, P: 0.005%, S: 0.001%, Cr: 1.03%, Mo: 0.26%, A1: 0.026%, Nb: 0.025%, Ti: 0.020%, Ni: 0.18%, Cu: 0.01%, B: 0.0005%, H: 0.000058%, N: 0.0056%, O: 0.0012%, the balance Fe and inevitable impurities.

3. The alloy steel for the ultra-high pressure gas cylinder according to claim 1 or 2, wherein yield strength of the alloy steel for the ultra-high pressure gas cylinder is 980 MPa or above, tensile strength of the alloy steel for the ultra-high pressure gas cylinder is 1100 MPa or above, and a -50°C low-temperature impact value of the alloy steel for the ultra-high pressure gas cylinder is 50 J / cm2 or above.

4. A preparation method of alloy steel for an ultra-high pressure gas cylinder, comprising: performing smelting, die casting and rolling to obtain an alloy steel plate for the ultra-high pressure gas cylinder, wherein during smelting, chemical compositions of the steel are controlled to be, by mass percentage: C: 0.32-0.36%, Si: 0.15-0.30%, Mn: 0.60-0.80%, Cr: 0.95-1.15%, Mo: 0.20-0.30%, A1: 0.02-0.04%, Nb: 0.015-0.025%, Ti: 0.015-0.025%, P≤0.007%, S≤0.005%, Ni: 0.12-0.20%, Cu≤0.10%, Sn≤0.005%, As≤0.005%, H≤0.00015%, N≤0.007%, O≤0.002%, the balance Fe and inevitable impurities, wherein P+S≤0.012% and Nb+V+Ti+B+Zr≤0.10%; and performing heat treatment on the alloy steel plate for the ultra-high pressure gas cylinder, wherein the heat treatment is performed through normalizing + quenching + tempering, and comprises the following specific processes: normalizing pretreatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in a high-temperature furnace and heated to 860±5°C, and after heat preservation time of 60-90 min, the alloy steel plate is naturally cooled to 25°C or below in air outside the furnace, or the alloy steel plate is subjected to accelerated cooling to 25°C or below through water-mist cooling or cold-air-blowing forced air cooling outside the furnace; quenching treatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in the high-temperature furnace and heated to 860±5°C at a heating speed of 3-5°C / min, and after heat preservation time of 60-90 min, the steel plate is soaked in water to be cooled to a room temperature; and high-temperature tempering treatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in a tempering furnace and heated to 560±5°C, and after heat preservation time of 120-150 min, the alloy steel plate is cooled to the room temperature in air outside the furnace.

5. The preparation method of the alloy steel for the ultra-high pressure gas cylinder according to claim 4, wherein: the alloy steel for the ultra-high pressure gas cylinder is smelted using 80-ton electric furnace smelting + LF furnace refining + a VD process, wherein the alloy steel has chemical compositions, by mass percentage: C: 0.33%, Si: 0.22%, Mn: 0.70%, P: 0.005%, S: 0.001%, Cr: 1.03%, Mo: 0.26%, A1: 0.026%, Nb: 0.025%, Ti: 0.020%, Ni: 0.18%, Cu: 0.01%, B: 0.0005%, H: 0.000058%, N: 0.0056%, O: 0.0012%, the balance Fe and inevitable impurities; and the alloy steel for the ultra-high pressure gas cylinder is die-cast into a blank, the blank is rolled to obtain the alloy steel plate for the ultra-high pressure gas cylinder with a thickness of 20 mm, and the alloy steel plate for the ultra-high pressure gas cylinder is subjected to heat treatment, comprising the following specific processes: normalizing pretreatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in a high-temperature furnace and heated to 860°C, and after heat preservation of 60 min, the alloy steel plate is naturally cooled to a room temperature of 23°C in air outside the furnace; quenching treatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in the high-temperature furnace and heated to 860°C at a heating speed of 3-5°C / min, and after heat preservation of 60 min, the steel plate is soaked in water to be cooled to a room temperature; and high-temperature tempering treatment: the alloy steel plate for the ultra-high pressure gas cylinder is placed in a tempering furnace and heated to 560°C, and after heat preservation of 120 min, the alloy steel plate is cooled to the room temperature in air outside the furnace.

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