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

Abstract

Alloy steel for an ultra-high pressure gas cylinder. The chemical composition of the alloy steel is controlled to be, in percentages by mass: 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%, and O≤0.002%, wherein P+S≤0.012% and Nb+V+Ti+B+Zr≤0.10%, with the balance being Fe and inevitable impurities. In the preparation method, the alloy steel for an ultra-high pressure gas cylinder is subjected to a heat treatment by means of a normalizing + quenching + tempering method, which method comprises: a normalizing pretreatment, involving: performing heating to 860±5°C, performing heat preservation for 60-90 min, then performing discharge from a furnace, and performing cooling to 25°C or below; a quenching treatment, involving: performing heating to 860±5°C, performing heat preservation for 60-90 min, and then performing water cooling to room temperature; and a high-temperature tempering treatment, involving: performing heating to 560±5°C, performing heat preservation for 120-150 min, then performing discharge from a furnace, and performing air cooling to room temperature. With regard to the alloy steel for an ultra-high pressure gas cylinder, the yield strength reaches 980 MPa or above, the tensile strength reaches 1100 MPa or above, the -50°C low-temperature impact value reaches 50 J / cm2 or above, and thus the alloy steel is suitable for manufacturing an ultra-high pressure gas cylinder.

Description

Alloy steel for ultra-high pressure gas cylinders and preparation method thereof Technical Field

[0001] The present invention belongs to the technical field of alloy steel for gas cylinders, and in particular relates to alloy steel for ultra-high pressure gas cylinders and a preparation method thereof. Background Art

[0002] Ultra-high-pressure gas cylinders with a working pressure of 30MPa are used to fill compressed gases such as O2, N2, Ar, He, H2 and CNG. Their designed wall thickness is thinner than that of high-pressure gas cylinders designed with general materials, which realizes the lightweighting of high-pressure gas cylinders, saves resources, reduces transportation losses, greatly increases the gas loading capacity of a single high-pressure gas cylinder, provides favorable conditions for the use of gas, and is widely used in industrial, civil and national defense fields.

[0003] In the existing technology, 34CrMo4 alloy steel is commonly used to make gas cylinders. However, 34CrMo4 alloy steel is only suitable for ordinary gas cylinders with a working pressure of 15MPa. Due to its low material strength, insufficient low-temperature impact resistance and short service life, it is difficult to be used in the manufacture of ultra-high pressure gas cylinders.

[0004] Summary of the Invention

[0005] In order to solve the technical problems existing in the above-mentioned prior art, the present invention provides an alloy steel for ultra-high pressure gas cylinders and a preparation method thereof. By designing the alloy steel composition and optimizing the heat treatment process, the strength and impact performance of the steel are improved, making it suitable for the manufacture and use of ultra-high pressure gas cylinders.

[0006] In one aspect of the present invention, an alloy steel for ultra-high pressure gas cylinders is provided, wherein the chemical composition of the alloy steel for ultra-high pressure gas cylinders is controlled as follows 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%, Al: 0.02-0.04%, Nb: 0.015-0.025%, T i: 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%, and P+S≤0.012%, Nb+V+Ti+B+Zr≤0.10%, the balance is Fe and unavoidable impurities.

[0007] Furthermore, in the above-mentioned alloy steel for ultra-high pressure gas cylinders, the chemical composition of the alloy steel for ultra-high pressure gas cylinders is as follows by mass percentage: C: 0.33%, Si: 0.22%, Mn: 0.70%, P: 0.005%, S: 0.001%, Cr: 1.03%, Mo: 0.26%, Al: 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%, and the balance is Fe and unavoidable impurities.

[0008] Furthermore, in the above-mentioned alloy steel for ultra-high pressure gas cylinders, the yield strength of the alloy steel for ultra-high pressure gas cylinders is above 980 MPa, the tensile strength is above 1100 MPa, the low temperature impact value at -50°C is above 50 J / cm 2 above.

[0009] In another aspect of the present invention, a method for preparing alloy steel for ultra-high pressure gas cylinders is provided, comprising:

[0010] The alloy steel plate for ultra-high pressure gas cylinders is obtained through smelting, die casting and rolling. The chemical composition of the steel is controlled by mass percentage as follows during smelting: 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%, Al: 0.02-0.04%, Nb: 0.015-0.025%, Ti: 0. : 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%, and P+S≤0.012%, Nb+V+Ti+B+Zr≤0.10%, the balance being Fe and unavoidable impurities;

[0011] The alloy steel plate for the ultra-high pressure gas cylinder is heat treated by normalizing + quenching + tempering. The specific process includes:

[0012] Normalizing pretreatment: Place the alloy steel plate for ultra-high pressure gas cylinders in a high-temperature furnace, heat it to 860±5℃, and keep it warm for 60-90 minutes. After the holding time is up, take it out of the furnace and let it cool naturally in the air to below 25℃, or use water mist cooling or strong air cooling with cold air to accelerate the cooling to below 25℃.

[0013] Quenching treatment: Place the alloy steel plate for ultra-high pressure gas cylinders in a high-temperature furnace and heat it to 860±5℃ at a heating rate of 3-5℃ / min. Keep it warm for 60-90min. After the holding time is up, soak the steel plate in water and cool it to room temperature.

[0014] High-temperature tempering treatment: Place the alloy steel plate for ultra-high pressure gas cylinders in a tempering furnace, heat it to 560±5℃, and keep it warm for 120-150 minutes. After the holding time is up, take it out of the furnace and cool it to room temperature in the air.

[0015] Furthermore, in the above-mentioned method for preparing alloy steel for ultra-high pressure gas cylinders, an 80-ton electric furnace smelting + LF furnace refining + VD degassing process is used to smelt the alloy steel for ultra-high pressure gas cylinders, and the chemical composition thereof is as follows by mass percentage: C: 0.33%, Si: 0.22%, Mn: 0.70%, P: 0.005%, S: 0.001%, Cr: 1.03%, Mo: 0.26%, Al: 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%, and the balance is Fe and unavoidable impurities; the ultra-high pressure gas cylinders are Alloy steel is die-cast into a billet, which is rolled to obtain an alloy steel plate for ultra-high-pressure gas cylinders with a thickness of 20 mm. The alloy steel plate for ultra-high-pressure gas cylinders is heat-treated, and the specific process includes: normalizing pretreatment, placing the alloy steel plate for ultra-high-pressure gas cylinders in a high-temperature furnace, heating it to 860°C, keeping it warm for 60 minutes, taking it out of the furnace and naturally cooling it to room temperature 23°C in the air; quenching treatment, placing the alloy steel plate for ultra-high-pressure gas cylinders in a high-temperature furnace, heating it to 860°C at a heating rate of 3-5°C / min, keeping it warm for 60 minutes, and then immersing the steel plate in water and cooling it to room temperature; high-temperature tempering treatment, placing the alloy steel plate for ultra-high-pressure gas cylinders in a tempering furnace, heating it to 560°C, keeping it warm for 120 minutes, and then taking it out of the furnace and cooling it to room temperature in the air.

[0016] The alloy steel for ultra-high pressure gas cylinders and the preparation method thereof of the present invention have the following advantages and beneficial effects:

[0017] By designing the alloy steel composition and optimizing the heat treatment process, the yield strength of the steel reaches above 980MPa, the tensile strength reaches above 1100MPa, and the low-temperature impact value at -50℃ reaches 50J / cm 2 The above-mentioned features significantly improve the yield strength, tensile strength and low-temperature impact performance, making it fully suitable for the manufacture and use of ultra-high pressure gas cylinders, and meeting the high quality, long life and lightweight requirements of the ultra-high pressure gas cylinder industry. DETAILED DESCRIPTION

[0018] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the embodiments described are only 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 ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] The alloy composition in steel determines its physical properties, chemical properties, and processing performance. Only the appropriate alloy content ratio can make it have excellent performance and meet production and application requirements. Therefore, in order to achieve the purpose of improving the strength and impact performance of steel in the present invention, the alloy composition of steel for gas cylinders must be optimized. To this end, the inventors designed the composition of alloy steel for ultra-high pressure gas cylinders by increasing the content of niobium and titanium in the steel. Titanium fixes nitrogen and sulfur, refines the structure of the cast matrix, plays a role in grain refinement, and improves the strength of the steel. The grains are further refined by normalizing treatment. When normalizing at an appropriately high temperature, high-melting point carbides are precipitated and dispersed and refined. During the cooling process, they further play a role in dispersion strengthening, which significantly improves the plasticity and impact toughness of the steel. Niobium has a strong inhibitory effect on recrystallization. The solute drag effect of undissolved niobium carbonitrides and dissolved niobium inhibits austenite recrystallization and refines ferrite grains. Another important function of niobium is to achieve precipitation strengthening effect. The addition of niobium and titanium interacts to reduce the activity of carbonitrides and increase their solubility, thereby increasing their stability in austenite, reducing their precipitation tendency, lowering precipitation temperatures, and resulting in finer precipitated particles. Overall, niobium and titanium can improve the strength and toughness of steel. Their combination with other alloying elements can achieve even more comprehensive performance improvements.

[0020] In addition, heat treatment of steel is a method of obtaining the desired microstructure and properties by heating it to a given temperature in the solid state, holding it for a period of time, and then cooling it at a specific rate and method. Normalizing, as a pre-heat treatment before quenching, heats the steel to 30-50°C above the Ac3 temperature, holds it for a period of time, and then air-cools it. This can eliminate the overheated coarse-grained structure and Widmanstätten structure in the casting and refine the grains. Quenching is heating the steel to a temperature above Ac3, holding it for a period of time to austenitize it, and then rapidly cooling it to below Ms at a rate greater than the critical cooling rate to undergo martensitic transformation. High-temperature tempering is heating the steel to 500-650°C after quenching, holding it for a period of time, and then cooling it at an appropriate rate. After high-temperature tempering, the carbide morphology in the material structure changes from flake to fine granular, and the distribution changes from uneven to dispersed, thereby improving the material's impact toughness.

[0021] As an embodiment of the present invention, the chemical composition of the alloy steel for ultra-high pressure gas cylinders of the present invention is controlled by mass percentage as follows: 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%, Al: 0.02-0.04%, Nb: 0.015-0.025%, Ti: 0.01 5~0.025%, 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%, and P+S≤0.012%, Nb+V+Ti+B+Zr≤0.10%, the balance is Fe and unavoidable impurities.

[0022] Furthermore, the alloy steel for ultra-high pressure gas cylinders of the present invention has a yield strength of more than 980 MPa, a tensile strength of more than 1100 MPa, and a low-temperature impact value of -50°C of 50 J / cm 2 above.

[0023] As an embodiment of the present invention, the method for preparing alloy steel for ultra-high pressure gas cylinders of the present invention comprises:

[0024] The alloy steel plate for ultra-high pressure gas cylinders is obtained through smelting, die casting and rolling. The chemical composition of the steel is controlled by mass percentage as follows during smelting: 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%, Al: 0.02-0.04%, Nb: 0.015-0.025%, Ti: 0. : 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%, and P+S≤0.012%, Nb+V+Ti+B+Zr≤0.10%, the balance being Fe and unavoidable impurities;

[0025] The alloy steel plate for ultra-high pressure gas cylinder is heat treated by normalizing + quenching + tempering. The specific implementation process includes the following steps:

[0026] Normalizing pretreatment: Place the alloy steel plate for ultra-high pressure gas cylinders in a high-temperature furnace, heat to 860±5℃, and keep warm for 60-90 minutes. After the holding time is up, take it out of the furnace and cool it to below 25℃.

[0027] Quenching treatment: Place the alloy steel plate for ultra-high pressure gas cylinders in a high-temperature furnace and heat it to 860±5℃ at a heating rate of 3-5℃ / min. Keep it warm for 60-90min. After the holding time is up, soak the steel plate in water and cool it to room temperature.

[0028] High-temperature tempering treatment: Place the alloy steel plate for ultra-high pressure gas cylinders in a tempering furnace, heat it to 560±5℃, and keep it warm for 120-150 minutes. After the holding time is up, take it out of the furnace and cool it to room temperature in the air.

[0029] As a specific embodiment, in the method for preparing alloy steel for ultra-high pressure gas cylinders of the present invention, after the normalizing pretreatment holding time is reached, it can be taken out of the furnace and naturally cooled in the air to below 25°C, or it can be taken out of the furnace and accelerated to below 25°C using strong air cooling methods such as water mist cooling or blowing cold air.

[0030] After testing, the yield strength of the alloy steel for ultra-high pressure gas cylinders prepared by the method for preparing alloy steel for ultra-high pressure gas cylinders of the present invention reaches above 980MPa, the tensile strength reaches above 1100MPa, and the low temperature impact value at -50℃ reaches 50J / cm 2 above.

[0031] The alloy steel for ultra-high pressure gas cylinders and the preparation method thereof of the present invention are described in detail below with reference to specific embodiments.

[0032] In an embodiment of the present invention, an 80-ton electric furnace smelting + LF furnace refining + VD degassing process is adopted to smelt alloy steel for ultra-high pressure gas cylinders, and the chemical composition thereof is as follows by mass percentage: C: 0.33%, Si: 0.22%, Mn: 0.70%, P: 0.005%, S: 0.001%, Cr: 1.03%, Mo: 0.26%, Al: 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%, and the balance is Fe and unavoidable impurities.

[0033] The alloy steel for ultra-high pressure gas cylinders is die-cast into a blank, and rolled to obtain an alloy steel plate for ultra-high pressure gas cylinders having a thickness of 20 mm. The alloy steel plate for ultra-high pressure gas cylinders is heat-treated, and the specific process includes:

[0034] Normalizing pretreatment: Place the alloy steel plate for ultra-high pressure gas cylinders in a high-temperature furnace, heat it to 860°C, keep it warm for 60 minutes, then take it out of the furnace and naturally cool it to room temperature 23°C in the air;

[0035] Quenching treatment: Place the alloy steel plate for ultra-high pressure gas cylinders in a high-temperature furnace, heat it to 860°C at a heating rate of 3-5°C / min, keep it at that temperature for 60 minutes, and then immerse the steel plate in water and cool it to room temperature;

[0036] High temperature tempering treatment: Place the alloy steel plate for ultra-high pressure gas cylinders in a tempering furnace, heat it to 560°C, keep it warm for 120 minutes, then take it out of the furnace and cool it to room temperature in the air.

[0037] The test results show that the yield strength of the alloy steel for ultra-high pressure gas cylinders prepared by the above embodiment of the present invention is 1058 MPa, the tensile strength is 1136 MPa, and the low-temperature impact value at -50°C is 51 J / cm 2 .

[0038] In summary, the alloy steel for ultra-high pressure gas cylinders and its preparation method of the present invention achieve a yield strength of more than 980 MPa, a tensile strength of more than 1100 MPa, and a low-temperature impact value of 50 J / cm at -50°C by designing the alloy steel composition and optimizing the heat treatment process. 2 The above-mentioned features significantly improve the yield strength, tensile strength and low-temperature impact performance, making it fully suitable for the manufacture and use of ultra-high pressure gas cylinders, and meeting the high quality, long life and lightweight requirements of the ultra-high pressure gas cylinder industry.

[0039] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. An alloy steel for ultra-high pressure gas cylinders, characterized in that: The chemical composition of the alloy steel for ultra-high pressure gas cylinders is controlled as follows 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%, Al: 0.02-0.04%, Nb: 0.015-0.025%, Ti: 0.015-0.02 5%, 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%, and P+S≤0.012%, Nb+V+Ti+B+Zr≤0.10%, the balance is Fe and unavoidable impurities.

2. The alloy steel for ultra-high pressure gas cylinders according to claim 1, characterized in that: The chemical composition of the alloy steel for ultra-high pressure gas cylinders is as follows by mass percentage: C: 0.33%, Si: 0.22%, Mn: 0.70%, P: 0.005%, S: 0.001%, Cr: 1.03%, Mo: 0.26%, Al: 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%, and the balance is Fe and unavoidable impurities.

3. The alloy steel for ultra-high pressure gas cylinders according to claim 1 or 2, characterized in that: The yield strength of the alloy steel for ultra-high pressure gas cylinders is above 980MPa, the tensile strength is above 1100MPa, and the low temperature impact value at -50℃ is above 50J / cm 2 above.

4. A method for preparing alloy steel for ultra-high pressure gas cylinders, characterized in that: include: The alloy steel plate for ultra-high pressure gas cylinders is obtained through smelting, die casting and rolling. The chemical composition of the steel is controlled by mass percentage as follows during smelting: 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%, Al: 0.02-0.04%, Nb: 0.015-0.025%, Ti:

0. : 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%, and P+S≤0.012%, Nb+V+Ti+B+Zr≤0.10%, the balance being Fe and unavoidable impurities; The alloy steel plate for the ultra-high pressure gas cylinder is heat treated by normalizing + quenching + tempering. The specific process includes: Normalizing pretreatment: Place the alloy steel plate for ultra-high pressure gas cylinders in a high-temperature furnace, heat it to 860±5℃, and keep it warm for 60-90 minutes. After the holding time is up, take it out of the furnace and let it cool naturally in the air to below 25℃, or use water mist cooling or strong air cooling with cold air to accelerate the cooling to below 25℃. Quenching treatment: Place the alloy steel plate for ultra-high pressure gas cylinders in a high-temperature furnace and heat it to 860±5℃ at a heating rate of 3-5℃ / min. Keep it warm for 60-90min. After the holding time is up, soak the steel plate in water and cool it to room temperature. High-temperature tempering treatment: Place the alloy steel plate for ultra-high pressure gas cylinders in a tempering furnace, heat it to 560±5℃, and keep it warm for 120-150 minutes. After the holding time is up, take it out of the furnace and cool it to room temperature in the air.

5. The method for preparing alloy steel for ultra-high pressure gas cylinders according to claim 4, characterized in that: The alloy steel for ultra-high pressure gas cylinders is smelted using an 80-ton electric furnace smelting + LF furnace refining + VD degassing process. The chemical composition, by mass percentage, is as follows: C: 0.33%, Si: 0.22%, Mn: 0.70%, P: 0.005%, S: 0.001%, Cr: 1.03%, Mo: 0.26%, Al: 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%, and the balance is Fe and unavoidable impurities. The alloy steel for ultra-high pressure gas cylinders is die-cast into a blank, and rolled to obtain an alloy steel plate for ultra-high pressure gas cylinders having a thickness of 20 mm. The alloy steel plate for ultra-high pressure gas cylinders is heat-treated, and the specific process includes: Normalizing pretreatment: put the alloy steel plate for ultra-high pressure gas cylinder into a high temperature furnace, heat it to 860℃, keep it at this temperature for 60 minutes, then take it out of the furnace and let it cool naturally to room temperature 23℃ in the air; For quenching treatment, the alloy steel plate for ultra-high pressure gas cylinders is placed in a high-temperature furnace and heated to 860°C at a heating rate of 3-5°C / min. After holding the temperature for 60 minutes, the steel plate is immersed in water and cooled to room temperature. For high temperature tempering treatment, the alloy steel plate for ultra-high pressure gas cylinders is placed in a tempering furnace, heated to 560°C, kept warm for 120 minutes, and then taken out of the furnace and cooled to room temperature in the air.