High-toughness economical gas cylinder pipe and manufacturing method thereof

Abstract

The invention discloses a high-toughness economical gas cylinder pipe, which contains Fe and inevitable impurities, and further contains the following chemical elements in percentage by mass: 0.34 to 0.37 percent of C, 0.17 to 0.30 percent of Si, 1.35 to 1.45 percent of Mn, less than or equal to 0.20 percent of Cu, less than or equal to 0.25 percent of Ni, 0.10 to 0.18 percent of Cr, 0.018 to 0.035 percent of Ti, 0.020 to 0.040 percent of Alt and 0.0015 to 0.0035 percent of B. The invention further discloses a manufacturing method of the high-toughness economical gas cylinder pipe. The manufacturing method comprises the steps that a pipe blank is manufactured; manufacturing the pipe blank into a steel pipe; quenching, wherein the quenching temperature is controlled to be 840-940 DEG C; tempering: controlling the tempering temperature to be 550-650 DEG C;

Description

Technical Field

[0001] The present invention relates to a steel pipe and a manufacturing method thereof, and in particular to a high-strength steel pipe and a manufacturing method thereof. Background Art

[0002] In actual use, the gas cylinder tube needs to be able to meet the requirements of high fatigue resistance and long service life during repeated charging and discharging of the energy storage device. Therefore, the gas cylinder tube for energy storage purposes has very high requirements for strength and toughness.

[0003] Existing gas cylinder tubes primarily use Cr-Mo steel to achieve this performance combination. However, its high alloy content, including the addition of precious metals such as Mo, leads to high costs, limiting its feasibility for large-scale engineering applications. Furthermore, the high alloy content also hinders the green nature of the product.

[0004] For example, Chinese patent publication CN105002445A, published on October 28, 2015, and titled "A 4130X seamless steel tube for manufacturing vehicle-mounted high-pressure gas cylinders and its preparation method," discloses a 4130X seamless steel tube for manufacturing vehicle-mounted high-pressure gas cylinders. The tube comprises the following: C: 0.28-0.34%, Si: 0.15-0.35%, Mn: 0.7-0.9%, Cr: 0.95-1.10%, Mo: 0.20-0.25%, Al: 0.010-0.040%, P ≤ 0.020%, S ≤ 0.010%, Ni ≤ 0.18%, Cu ≤ 0.20%, As + Sn + Sb + Bi + Pb ≤ 0.035%, with the remainder being iron and trace impurity elements. This indicates that the cylinders also use the Cr-Mo steel composition system.

[0005] For example, Chinese patent publication CN104120352A, published on October 29, 2014, and titled "34CrMo4 Steel for Gas Cylinders and Production Method Thereof," discloses 34CrMo4 steel for gas cylinders and its production method. The steel comprises: C: 0.33-0.36%, Si: 0.15-0.35%, Mn: 0.65-0.85%, Mo: 0.15-0.30%, Cr: 0.90-1.10%, Als: 0.015-0.050%, P ≤ 0.011 wt%, S ≤ 0.004%, H ≤ 0.00020%, with the remainder being Fe and unavoidable impurities. This also reflects the Cr-Mo steel composition system. Summary of the Invention

[0006] One of the purposes of the present invention is to provide a high-strength and tough economical gas cylinder tube, which has high strength and good low-temperature toughness resistance while reducing costs and having good economic benefits.

[0007] In order to achieve the above object, the present invention provides a high-strength, tough and economical gas cylinder tube, which contains Fe and inevitable impurities, and in addition, it also contains the following chemical elements in the following mass percentages:

[0008] C: 0.34 - 0.37%, Si: 0.17 - 0.30%, Mn: 1.35 - 1.45%, Cu ≤ 0.20%, Ni ≤ 0.25%, Cr: 0.10 - 0.18%, Ti: 0.018 - 0.035%, Alt: 0.020 - 0.040%, B: 0.0015 - 0.0035%.

[0009] Furthermore, in the high-strength, tough and economical gas cylinder tube of the present invention, the mass percentages of its various chemical elements are as follows:

[0010] C: 0.34 - 0.37%, Si: 0.17 - 0.30%, Mn: 1.35 - 1.45%, Cu ≤ 0.20%, Ni ≤ 0.25%, Cr: 0.10 - 0.18%, Ti: 0.018 - 0.035%, Alt: 0.020 - 0.040%, B: 0.0015 - 0.0035%; the balance is Fe and inevitable impurities.

[0011] The present invention adopts an alloying scheme of adding trace amounts of Ti and B, and simultaneously adding a small amount of inexpensive metal Cr, which not only reduces the cost but also achieves high performance. Among them, the austenite grains during heating and hot working are refined by Ti to ensure the final degree of microstructure refinement, and the strength and toughness are improved simultaneously through the obtained fine grain effect; adding trace amounts of B realizes the improvement of hardenability, ensuring full hardening in the thickness direction of the material to obtain a uniform and consistent microstructure, thereby improving strength and toughness; adding a certain amount of inexpensive metal Cr further enhances the hardenability of the material, and at the same time, Cr can combine with C to form carbides of Cr, thereby further enhancing the strength of the material after tempering. In addition, in the present invention, by controlling the upper limits of the C and Mn contents not to be too high, serious segregation is avoided, and its influence on the performance uniformity in the wall thickness direction and the final overall low-temperature impact toughness is avoided.

[0012] Specifically, in the high-strength, tough and economical gas cylinder tube of the present invention, the design principles of its various chemical elements are as follows:

[0013] C: In the high-strength, tough and economical gas cylinder tube of the present invention, the C element is the most economical strengthening element in steel, and it enhances the strength of the steel through interstitial solid solution strengthening, precipitation strengthening and phase transformation strengthening. Increasing the carbon content can significantly improve the hardenability of the steel, reduce the addition amount of other precious alloys, and reduce the production cost. Based on this, a design with a relatively high C is adopted in the present invention, and the mass percentage content of the C element is controlled between 0.34 - 0.37%.

[0014] Si: In the high-strength, tough and economical gas cylinder tube of the present invention, the Si element is a solid solution strengthening element and also a deoxidizing element in the steel. However, when the content of the Si element is too high, it will have an adverse effect on the surface quality and low-temperature toughness of the steel. When the content of the Si element exceeds 0.30%, the toughness of the steel will decrease. Based on this, in the high-strength, tough and economical gas cylinder tube of the present invention, the mass percentage content of the Si element is controlled between 0.17% and 0.30%.

[0015] Mn: In the high-strength, tough and economical gas cylinder tube of the present invention, the Mn element improves the strength of the steel through solid solution strengthening and is the most important and economical strengthening element in the steel to compensate for the strength loss caused by the decrease in C content. The Mn element helps to obtain fine phase transformation products and is beneficial to improving low-temperature toughness. However, when the content of the Mn element is too low, it will aggravate the center segregation, and when it is excessive, it will cause the low-temperature toughness to decrease instead. Based on this, in the high-strength, tough and economical gas cylinder tube of the present invention, the mass percentage content of the Mn element is controlled between 1.35% and 1.45%.

[0016] Cu: In the high-strength, tough and economical gas cylinder tube of the present invention, the Cu element is a residual element brought in by scrap steel during the steel smelting process. When the content of the Cu element is too high, it is easy to cause hot cracks during the hot working process. Based on this, in the high-strength, tough and economical gas cylinder tube of the present invention, the mass percentage content of the Cu element is controlled below 0.20%.

[0017] Ni: In the high-strength, tough and economical gas cylinder tube of the present invention, the Ni element is a residual element brought in by scrap steel during the steel smelting process. The Ni element can improve the toughness of the steel, but when the content of the Ni element is too high, it will lower the ferrite-austenite phase transformation point, which is not conducive to the process means of improving the performance by high-temperature tempering. Based on this, in the high-strength, tough and economical gas cylinder tube of the present invention, the mass percentage content of the Ni element is controlled within 0.25%.

[0018] Cr: In the high-strength, tough and economical gas cylinder tube of the present invention, the Cr element has a certain solid solution strengthening effect and can effectively improve the hardenability of the steel, and will inhibit the formation of ferrite transformation. At the same time, Cr is a strong carbide-forming element and can promote the precipitation of dissolved carbon in the form of carbides. However, when the content of the Cr element is too high, it is not conducive to low-temperature toughness. Based on this, in the high-strength, tough and economical gas cylinder tube of the present invention, the mass percentage content of the Cr element is controlled between 0.10% and 0.18%.

[0019] Ti: In the high-strength, tough and economical gas cylinder tube described in the present invention, the Ti element is a good deoxidizer and degasser and an effective element for fixing nitrogen and carbon. The undissolved carbonitrides of the Ti element can prevent the growth of austenite grains during steel heating. The TiN and TiC precipitated during rough rolling in the high-temperature austenite region can effectively inhibit the growth of austenite grains, thus refining the grains, and providing a refined initial structure for subsequent hot working and heat treatment processes, which is beneficial for the final product to obtain a refined structure. However, when the Ti content is too high, it is easy to form TiN particles with larger sizes, resulting in an adverse effect of reducing low-temperature toughness similar to that of larger inclusions. Based on this, in the high-strength, tough and economical gas cylinder tube described in the present invention, the mass percentage content of the Ti element is controlled between 0.018% and 0.035%.

[0020] Alt: In the high-strength, tough and economical gas cylinder tube described in the present invention, the Al element is used for deoxidizing the steel grade. Appropriate Al is also beneficial for refining the grains and improving the strength and toughness properties. However, when the Al element content is greater than 0.04%, it may form coarse precipitates, thus reducing the low-temperature toughness of the steel. Based on this, in the high-strength, tough and economical gas cylinder tube described in the present invention, the mass percentage content of the Al element is controlled between 0.020% and 0.040%.

[0021] B: In the high-strength, tough and economical gas cylinder tube described in the present invention, the main role of the B element in the steel is to increase the hardenability and strength of the steel, thus saving other rarer and more expensive metals. However, the addition of the B element will have a significant adverse impact on the low-temperature toughness of the material. Based on this, in the high-strength, tough and economical gas cylinder tube described in the present invention, the mass percentage content of the B element is controlled between 0.0015% and 0.0035%.

[0022] Furthermore, in the high-strength, tough and economical gas cylinder tube described in the present invention, it also contains V ≤ 0.05 wt%.

[0023] In the present invention, the vanadium element mainly exists in the form of carbides in the steel, which can strongly improve the strength of the steel. However, when the V element content is too high, it will cause a decrease in the toughness of the steel. Based on this, in the high-strength, tough and economical gas cylinder tube described in the present invention, the mass percentage content of the V element is controlled below 0.05%.

[0024] Furthermore, in the inevitable impurities of the high-strength, tough and economical gas cylinder tube described in the present invention, the mass percentage content of each impurity element satisfies: P ≤ 0.015%, S ≤ 0.008%, P + S ≤ 0.02%, O ≤ 0.0025%, N ≤ 0.007%, H ≤ 0.0002%.

[0025] In the present invention, the inevitable impurities are mainly S, P, O, N and H. Under the condition permitted by the technical conditions, it is expected that their contents are as low as possible.

[0026] Among them, phosphorus is likely to cause cold brittleness of steel, and sulfur is likely to cause hot brittleness, resulting in unstable properties of steel. As the S content increases, the MnS inclusions increase, significantly reducing the low-temperature toughness of the material. Based on this, in some embodiments of the present invention, on the basis of controlling P≤0.015% and S≤0.008%, P+S≤0.020% is also controlled.

[0027] In addition, when the contents of O, N, and H are too high, they are unfavorable to the low-temperature toughness and fatigue resistance of the material. Based on this, in some embodiments of the present invention, O≤0.0025%, N≤0.007%, and H≤0.0002% can be controlled.

[0028] Furthermore, the microstructure of the high-strength and high-toughness economical gas cylinder tube described in the present invention is tempered sorbite.

[0029] Furthermore, the properties of the high-strength and high-toughness economical gas cylinder tube described in the present invention meet the following requirements: yield strength ≥520 MPa, tensile strength ≥800 MPa, elongation ≥16%, KV2 at -40°C ≥47 J, and lateral expansion amount LE≥0.53 mm.

[0030] Even further, the properties of the high-strength and high-toughness economical gas cylinder tube described in the present invention meet the following requirements: yield strength ≥560 MPa, tensile strength ≥830 MPa, elongation ≥21%, KV2 at -40°C ≥65 J, and lateral expansion amount LE≥0.7 mm.

[0031] Another object of the present invention is to provide a manufacturing method of a high-strength and high-toughness economical gas cylinder tube, and this manufacturing method has a simple process and low cost.

[0032] To achieve the above object, the present invention also provides a manufacturing method of a high-strength and high-toughness economical gas cylinder tube, including the steps of:

[0033] (1) Produce a tube blank;

[0034] (2) Make the tube blank into a steel pipe;

[0035] (3) Quenching: Control the quenching temperature to be 840 - 940°C;

[0036] (4) Tempering: Control the tempering temperature to be 550 - 650°C.

[0037] The present invention obtains a martensite structure through the quenching step, and then further forms a tempered sorbite structure through the tempering step, thereby reducing the strength and improving the low-temperature toughness.

[0038] In the present invention, the quenching temperature is controlled between 840°C and 940°C because, when the quenching temperature exceeds this upper limit, the austenite grains coarsen and grow. Large austenite grains are not conducive to the formation of fine phase transformation structure, which is detrimental to low-temperature toughness. When the quenching temperature is below this lower limit, the alloying elements are not fully dissolved, and the original coarse precipitates are not easily dissolved back to form fine precipitates in the subsequent process, resulting in strength that cannot meet the requirements. Based on this, the quenching temperature is controlled between 840°C and 940°C.

[0039] In the present invention, the tempering temperature is controlled between 550°C and 650°C because, when the tempering temperature is higher than the upper limit, the tempered martensite (tempered bainite) formed during quenching will significantly soften, resulting in a decrease in material strength. When the tempering temperature is lower than the lower limit, the steel body strength becomes too high, resulting in a decrease in toughness and plasticity. Therefore, the tempering temperature is controlled between 550°C and 650°C.

[0040] Furthermore, in step (3) of the high-strength and tough economical gas cylinder tube of the present invention, the heat preservation time is controlled to be 0.3 to 1.2 hours.

[0041] During the quenching process of the present invention, if the quenching time is too long, the austenite grains will coarsen and grow. Large austenite grains are not conducive to the formation of fine phase transformation structure, which is detrimental to low-temperature toughness. If the quenching time is too short, the alloying elements will not fully dissolve, and the original coarse precipitates will not easily dissolve back, forming fine precipitates in the subsequent process, resulting in strength that cannot meet the requirements. Based on this, the quenching and holding time is controlled to 0.3-1.2 hours.

[0042] Furthermore, in step (4) of the high-strength and tough economical gas cylinder tube of the present invention, the heat preservation time is controlled to be 0.3 to 1.2 hours.

[0043] During the tempering process of the present invention, if the tempering time is too long, the tempered martensite (tempered troostite) formed during quenching will significantly soften, resulting in a decrease in material strength. If the tempering time is too short, the strength is too high, resulting in a decrease in toughness and plasticity. Therefore, the tempering heating time is controlled to 0.3-1.2 hours.

[0044] Compared with the prior art, the high-strength and tough economical gas cylinder tube and its manufacturing method described in the present invention have the following advantages and beneficial effects:

[0045] The high-strength and tough economical gas cylinder tube described in the present invention adopts a simple component system and an alloying scheme of adding a small amount of cheap metal Cr, which reduces costs while also achieving high strength and good low-temperature toughness, meeting the performance requirements of gas cylinder tubes for energy storage applications such as compressed air energy storage.

[0046] In some preferred embodiments, the performance of the high-strength and tough economical gas cylinder tube of the present invention meets the following requirements: yield strength ≥ 560 MPa, tensile strength ≥ 830 MPa, elongation ≥ 21%, KV2 ≥ 65 J at -40°C, and lateral expansion LE ≥ 0.7 mm. DETAILED DESCRIPTION

[0047] The high-strength and tough economical gas cylinder tube of the present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an undue limitation to the technical solution of the present invention.

[0048] Examples 1-9 and Comparative Examples 1-7

[0049] The high-strength and tough economical gas cylinder tubes of Examples 1-9 and the comparative tubes of Comparative Examples 1-7 were all prepared by the following steps:

[0050] (1) Smelting and continuous casting into round tube billets, the composition of which is shown in Table 1.

[0051] (2) The tube blank is made into a steel tube with an outer diameter of 508 mm and a wall thickness of 16 mm.

[0052] (3) Quenching: Control the quenching temperature to 840-940°C and the holding time to 0.3-1.2h.

[0053] (4) Tempering: Control the tempering temperature to 550-650℃ and the holding time to 0.3-1.2h.

[0054] It should be noted that the high-strength, tough, and economical gas cylinder tubes of Examples 1-9 described herein were all produced using the above steps, and their chemical compositions and related process parameters all met the design specification control requirements of the present invention. The comparative tubes of Comparative Examples 1-7 were also produced using the above process flow, but the chemical compositions of the comparative tubes of Comparative Examples 1-3 did not meet the design requirements of the present invention, and the related process parameters of the comparative tubes of Comparative Examples 4-7 did not meet the design requirements of the present invention.

[0055] Table 1 lists the mass percentages of various chemical elements in the high-strength and economical gas cylinder tubes of Examples 1-9 and the control tubes of Comparative Examples 1-7.

[0056] Table 1. (wt%, the balance is Fe and other inevitable impurities except S, P, N, H, O)

[0057]

[0058]

[0059] Table 2 lists the specific process parameters of the quenching and tempering steps of the high-strength and tough economical gas cylinder tubes of Examples 1-9 and the control tubes of Comparative Examples 1-7.

[0060] Table 2

[0061] Number Quenching heating temperature (°C) Quenching heating time (h) Tempering temperature (°C) Tempering heating time (h) Example 1 840 1.2 550 1.2 Example 2 900 1.0 580 0.8 Example 3 940 0.3 650 0.3 Example 4 880 1.1 650 0.3 Example 5 910 0.9 590 0.8 Example 6 860 1.1 570 1.0 Example 7 920 0.8 630 0.5 Example 8 930 0.6 600 0.7 Example 9 940 0.4 610 0.6 Comparative Example 1 900 1.0 580 0.8 Comparative Example 2 900 1.0 580 0.8 Comparative Example 3 900 1.0 580 0.8 Comparative Example 4 960 1.0 580 0.8 Comparative Example 5 825 1.0 580 0.8 Comparative Example 6 900 1.0 530 0.8 Comparative Example 7 900 1.0 680 0.8

[0062] Samples were taken from the finally prepared high-strength, tough and economical gas cylinder tubes of Examples 1-9 and the comparative tubes of Comparative Examples 1-7, and tested. The obtained test results are listed in Table 3. The relevant test methods are as follows:

[0063] (1) Microstructure: The polished metallographic surface was etched with a 4% nitric acid alcohol solution, and the microstructure was observed with an optical microscope at a magnification of ×500.

[0064] (2) Tensile test: At room temperature, the longitudinal tensile properties were tested according to the method of Chinese national standard GB / T 228.1.

[0065] (3) Impact test: At a specified temperature (-40 °C), the transverse impact properties were tested according to the method of Chinese national standard GB / T 229.

[0066] Table 3 lists the test results of the high-strength, tough and economical gas cylinder tubes of Examples 1-9 and the comparative tubes of Comparative Examples 1-7.

[0067] Table 3

[0068]

[0069]

[0070] Note: The values of the -40 °C Charpy impact energy KV2 and the -40 °C Charpy impact lateral expansion in Table 3 above are all the values of three measurements.

[0071] It can be seen from Table 3 above that in the present invention, the main microstructure of the thick-specification high-strength, tough and economical gas cylinder tubes of Examples 1-6 prepared by using the technical solution designed by the present invention is tempered martensite (or tempered sorbite).

[0072] In addition, it can also be seen from Table 3 above that compared with the comparative tubes of Comparative Examples 1-7, the high-strength, tough and economical gas cylinder tubes of Examples 1-9 of the present invention have better performance, with a yield strength greater than 560 MPa, a tensile strength greater than 830 MPa, an elongation rate ≥ 21%, a KV2 ≥ 65 J at -40 °C, and a lateral expansion amount LE ≥ 0.7 mm.

[0073] Thus, it can be seen that the high-strength, tough and economical gas cylinder tubes described in the present invention have excellent performance.

[0074] It should be noted that the prior art part in the protection scope of the present invention is not limited to the embodiments given in this application document. All prior arts that do not conflict with the solution of the present invention, including but not limited to prior patent documents, prior published publications, prior public use, etc., can be included in the protection scope of the present invention.

[0075] In addition, the combination manner of each technical feature in this case is not limited to the combination manner recorded in the claims of this case or the combination manner recorded in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any manner, unless contradictions occur between them.

[0076] It should also be noted that the above-listed are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many similar variations. All deformations directly derived or associated by those skilled in the art from the content disclosed in the present invention shall fall within the protection scope of the present invention.

Claims

1. A high-strength, tough and economical gas cylinder tube, which contains Fe and inevitable impurities, is characterized in that, It also contains the following chemical elements in the following mass percentages: C: 0.34 - 0.37%, Si: 0.17 - 0.30%, Mn: 1.35 - 1.45%, Cu ≤ 0.20%, Ni ≤ 0.25%, Cr: 0.10 - 0.18%, Ti: 0.018 - 0.035%, Alt: 0.020 - 0.040%, B: 0.0015 - 0.0035%.

2. The high-strength, tough and economical gas cylinder tube according to claim 1, wherein The mass percentages of its various chemical elements are: C: 0.34 - 0.37%, Si: 0.17 - 0.30%, Mn: 1.35 - 1.45%, Cu ≤ 0.20%, Ni ≤ 0.25%, Cr: 0.10 - 0.18%, Ti: 0.018 - 0.035%, Alt: 0.020 - 0.040%, B: 0.0015 - 0.0035%; the balance is Fe and unavoidable impurities.

3. The high-strength, tough and economical gas cylinder tube according to claim 1, characterized in that It also contains V ≤ 0.05 wt%.

4. The high-strength, tough and economical gas cylinder tube according to claim 1, characterized in that, Among the unavoidable impurities, the mass percentage contents of each impurity element satisfy: P ≤ 0.015%, S ≤ 0.008%, P + S ≤ 0.02%, O ≤ 0.0025%, N ≤ 0.007%, H ≤ 0.0002%.

5. The high-strength, tough and economical gas cylinder tube according to claim 1 or 2, characterized in that, Its microstructure is tempered sorbite.

6. The high-strength, tough and economical gas cylinder tube according to claim 1 or 2, characterized in that, Its properties satisfy: yield strength ≥ 520 MPa, tensile strength ≥ 800 MPa, elongation ≥ 16%, KV2 at -40°C ≥ 47 J, lateral expansion amount LE ≥ 0.53 mm.

7. The high-strength, tough and economical gas cylinder tube according to claim 6, characterized in that, Its properties satisfy: yield strength ≥ 560 MPa, tensile strength ≥ 830 MPa, elongation ≥ 21%, KV2 at -40°C ≥ 65 J, lateral expansion amount LE ≥ 0.7 mm.

8. The manufacturing method of the high-strength and tough economical gas cylinder pipe according to any one of claims 1-7, characterized in that, It includes the steps: (1) Prepare a tube blank; (2) Make the tube blank into a steel pipe; (3) Quench: Control the quenching temperature to be 840 - 940°C; (4) Temper: Control the tempering temperature to be 550 - 650°C.

9. The manufacturing method according to claim 8, characterized in that, In step (3), control the holding time to be 0.3 - 1.2 h.

10. The manufacturing method according to claim 8, characterized in that, In step (4), control the holding time to be 0.3 - 1.2 h.

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