CN109423570B - Steel for low-temperature pressure vessel and manufacturing method thereof - Google Patents

Steel for low-temperature pressure vessel and manufacturing method thereof Download PDF

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CN109423570B
CN109423570B CN201710731755.2A CN201710731755A CN109423570B CN 109423570 B CN109423570 B CN 109423570B CN 201710731755 A CN201710731755 A CN 201710731755A CN 109423570 B CN109423570 B CN 109423570B
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steel
low
temperature
temperature pressure
pressure vessel
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CN109423570A (en
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郑宏光
徐国栋
王迎春
沈燕
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Baoshan Iron and Steel Co Ltd
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Baoshan Iron and Steel Co Ltd
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Priority to JP2020511260A priority patent/JP7024063B2/en
Priority to PCT/CN2018/101858 priority patent/WO2019037749A1/en
Priority to KR1020207006798A priority patent/KR102364473B1/en
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

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  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The invention discloses steel for a low-temperature pressure container, which comprises, by mass, 0.02-0.08% of C, 0.10-0.35% of Si, 0.3-0.8% of Mn, 7.0-12.0% of Ni, not more than 0.005% of N, 0.015-0.05% of Al, 0.1-0.3% of Nb, 0.1-0.3% of Ti, 0.001-0.005% of Mg, and the balance Fe and other inevitable impurities, wherein microstructures of the steel for the low-temperature pressure container are austenite structures from the beginning of solidification to the room temperature state, and accordingly the invention also discloses a manufacturing method of the steel for the low-temperature pressure container, which comprises the steps of (1) smelting in a converter, then L F + RH refining, (2) continuous casting, (3) hot rolling, (4) quenching heat treatment, and (5) tempering treatment.

Description

Steel for low-temperature pressure vessel and manufacturing method thereof
Technical Field
The present invention relates to steel and a method for manufacturing the same, and more particularly, to nickel-containing steel for a low temperature pressure vessel and a method for manufacturing the same.
Background
The 9% Ni steel is low carbon steel with about 9% of Ni element, originated from the product research laboratory of the American International Nickel company, the lowest using temperature can reach-196 ℃, 1952, the first 9% Ni steel storage tank is put into use in the United states, the first domestic liquefied natural gas low-temperature storage tank is built in 1969 in Japan, the maximum tank capacity of the built storage tank reaches 20 × l04m3. Along with the increasing of the newly-increased and proven reserves of natural gas in China, governments increasingly pay more attention to the development and utilization of natural gas and the design and construction of low-temperature storage equipment thereof. In the 20 th century, 8O's, in Daqing ethylene engineering, a large 9% Ni steel ethylene spherical tank was successfully built for the first time. In 2004, the first large-scale low-temperature liquefaction day in ChinaThe capacity of a single storage tank reaches 16 × 10 when a natural gas project, namely the Guangdong liquefied natural gas project, is started4m3. To date, 9% Ni steels have been used in lng plants for over 60 years. Because of its excellent low-temperature toughness and good welding performance, 9% Ni steel has become a widely used steel grade in the international low-temperature equipment field.
The low-temperature mechanical property of the 9% Ni steel is mainly determined by chemical components, particularly the content of Ni and C elements. In addition, the toughness of the steel depends on the purity of the steel and the microstructure.
The 9% Ni steel is produced by continuous casting steel-making process, and the metallurgy treatment, vacuum degassing process and high purity of steel in the steel-casting process play an extremely important role in improving the low-temperature toughness of the steel. Since the presence of impurity elements such as P and S deteriorates the low-temperature toughness of steel, the content of impurity elements such as P and S must be strictly controlled to a low level.
9% Ni steel was incorporated into JIS standards in 1977 in Japan. In the same year, the U.S. also included 9% Ni steel in ASME and ASTM standards. The code, chemical composition and mechanical properties of the 9% Ni steel in each major industrial country are shown in tables 1 and 2.
TABLE 1 chemical composition in wt% of related typical steel grades in the prior art
Figure BDA0001387272940000011
Figure BDA0001387272940000021
TABLE 2 mechanical Properties of the related typical Steel grades in the prior art
State of the country Yield strength Rel(MPa) Tensile strength Rm(MPa) Elongation (%) Impact toughness at-196 ℃ (J)
United states of America ≥585 690-825 20 ≥100
United states of America ≥585 690-825 18 ≥100
Germany 490 637-833 18 ≥100
Japanese ≥590 690-830 20 ≥100
Great Britain ≥590 690-830 20 ≥100
China (China) ≥575 680-820 20 ≥100
As can be seen from tables 1 and 2, the steels for cryogenic pressure vessels in the prior art are increasingly unable to meet the increasing requirements of use and manufacture. In view of the above, it is desirable to obtain a steel for a low temperature pressure vessel, which has improved mechanical properties and low temperature impact toughness compared to the prior art, and which is more economical to produce.
Disclosure of Invention
One of the objectives of the present invention is to provide a steel for a low temperature pressure vessel, which has a microalloy addition design, does not need to add too many expensive elements such as Ni, and controls the total oxygen content to be lower by adding appropriate amounts of Nb, Ti, and Mg elements, so that the steel for a low temperature pressure vessel has higher strength, good formability and low temperature impact toughness, and the cost of the steel material is lower compared with the prior art.
Based on the aim, the invention provides steel for a low-temperature pressure container, which comprises the following chemical elements in percentage by mass:
0.02-0.08% of C, 0.10-0.35% of Si, 0.3-0.8% of Mn, 7.0-12.0% of Ni, less than or equal to 0.005% of N, 0.015-0.05% of Al, 0.1-0.3% of Nb, 0.1-0.3% of Ti and 0.001-0.005% of Mg; the balance being Fe and other unavoidable impurities;
compared with the prior art, the steel for the low-temperature pressure vessel is formed by adding a proper amount of Nb (C, N), so that the strength is improved, and the impact toughness is improved; in addition, the low-temperature impact toughness of the steel can be obviously improved by adding Ti and Mg, and the effect of improving the strength of the steel is also considered.
In addition, according to the technical scheme of the invention, the microstructure of the steel for the low-temperature pressure container evolves as follows: the austenite structure is formed from the solidification of the continuous casting slab to the room temperature. After hot rolling, the main structure of the Quenching and Tempering (QT) heat treatment is low-carbon tempered martensite. Wherein, the quenching treatment can obtain martensite with fine crystal grains, the subsequent tempering treatment can convert the martensite structure into ferrite and fine precipitated carbide, and simultaneously can obtain a small amount of dispersed austenite, thereby greatly improving the toughness of the base material and being particularly suitable for manufacturing low-temperature-resistant and pressure-bearing parts.
The design principle of each chemical element of the steel for the low-temperature pressure container is as follows:
c: generally, the mass percent of C mainly affects the precipitation amount of carbides and the precipitation temperature range. In the steel for the low-temperature pressure container, carbon has a certain strengthening effect, and the control of the lower mass percent of C is beneficial to improving the impact toughness of the steel. However, too high a mass percentage of carbon may reduce the corrosion resistance of the material. In order to take mechanical property and impact toughness into consideration, the mass percent of C is controlled to be 0.02-0.08%.
Si: si may improve strength in steel, but it also may be disadvantageous in formability and toughness of steel. The steel for the low-temperature pressure container controls the mass percent of Si to be 0.10-0.35%.
Mn: mn is an austenite element, can inhibit the harmful effect of S in the nickel-based corrosion-resistant alloy and improve the thermoplasticity. However, too high a mass percentage of Mn is not favorable for securing the corrosion resistance. Therefore, the mass percentage of Mn in the low-temperature pressure vessel is limited to 0.3-0.8% by taking the mechanical properties and the corrosion resistance into comprehensive consideration.
Ni: ni is a main element in the steel for the low-temperature pressure container, has good austenite phase stability, and can improve the mechanical property and the impact toughness of the steel for the low-temperature pressure container. The high-temperature tensile strength gradually increases with the increase of Ni, because when the mass percentage of Ni is low, most of Ni is dissolved in austenite, the austenite phase region is enlarged, the recrystallization temperature is increased, and the mechanical property of the alloy is improved. Therefore, the mass percentage of Ni in the steel for a low-temperature pressure vessel according to the present invention is limited to 7.0 to 12.0%.
N: n is a stable austenite element. The control of the N with lower mass percentage is beneficial to improving the impact toughness of the steel for the low-temperature pressure container. However, a higher mass percentage of nitrogen tends to reduce the toughness and ductility of the steel, and also reduces the hot workability of the steel. Therefore, the mass percentage of N in the steel for a low-temperature pressure vessel according to the present invention is limited to N.ltoreq.0.005%.
Al: in the technical scheme of the invention, the oxygen content in the steel is mainly controlled by Al, so that the dislocation behavior is influenced to strengthen the alloy. Increasing the mass percent of Al can significantly increase the solution temperature, creep strength, but too high a mass percent of Al compromises the plasticity of the steel. In addition, the addition of Al is beneficial to improving the elongation deformation performance of the steel, thereby improving the processing performance of the steel. However, the Al content required to be higher than 0.05% by mass lowers the impact toughness of the steel. In view of the above, the mass percentage of Al in the steel for a low-temperature pressure vessel according to the present invention is limited to 0.015 to 0.05%.
Nb: nb is one of the commonly used solid-solution strengthening elements. The atomic radius of Nb is 15-18% larger than that of Ni, Co and Fe atoms, and in addition, Nb is a strong carbonitride forming element and is combined with carbon and nitrogen to form Nb (C, N), thereby being beneficial to improving the strength and the impact toughness. Meanwhile, carbon and nitrogen have certain strengthening effect, and part of Nb in the steel forms Nb (C, N) which can strengthen an austenite phase matrix, refine austenite grains and strengthen austenite grain boundaries, thereby being beneficial to improving the low-temperature impact toughness of the steel for the low-temperature pressure container. Therefore, the mass percentage of Nb in the steel for a low-temperature pressure vessel according to the invention is limited to 0.1 to 0.3%.
Ti: ti has the functions of solid solution strengthening and precipitation strengthening in steel, has strong binding capacity with O, and can reduce the oxygen content in the steel. In addition, Ti combines with C, N to form Ti (C, N), which can refine the coagulated structure. In alloys containing higher amounts of Ni, especially in the combined action of Nb and Al, the addition of Ti results in the formation of Ni3(Al, Ti, Nb), which improves the strength and toughness of the steel.
Mg: the trace magnesium is subjected to segregation at the grain boundary to reduce the grain boundary energy and the phase boundary energy, improve and refine the forms of grain boundary carbides and other grain boundary precipitated phases, for example, the carbides are made into blocks or spheroidized, so that the grain boundary sliding is effectively inhibited, the stress concentration of the grain boundary is reduced, and the notch sensitivity is eliminated. In addition, magnesium and harmful impurities such as sulfur form high-melting-point compounds such as MgO and MgS, etc., so that grain boundaries are purified, the concentration of impurity elements such as S, O, P in the grain boundaries is obviously reduced, and the harm of the impurity elements is reduced. During solidification, MgO, MgS and the like in the steel can be used as nucleation particles to refine grains. The trace magnesium improves the plasticity, improves the high-temperature tensile plasticity and increases the impact toughness and the fatigue strength.
In the invention, the inevitable impurity elements include O, P and S. For the technical scheme of the invention, O mainly exists in oxide inclusions, the total oxygen content is high, which indicates that the inclusions are more, and the reduction of the total oxygen content is beneficial to improving the comprehensiveness of the material, so that the mass percentages of the steel for the low-temperature pressure container for the inevitable impurity elements are controlled as follows: total oxygen is less than or equal to 0.001 percent, P is less than or equal to 0.010 percent, and S is less than or equal to 0.005 percent.
Further, in the steel for the low-temperature pressure vessel, the chemical elements also comprise at least one of Ce, Hf, L a, Re, Sc and Y, and the total mass percentage of the elements is less than or equal to 1 percent.
In the technical scheme of the invention, the rare earth elements comprise Ce, Hf, L a, Re, Sc and Y, the rare earth elements are used as purifying agents and have the functions of deoxidation and desulfurization, so that the harmful effects of oxygen and sulfur on grain boundaries are reduced, in addition, the rare earth elements are used as micro-alloying elements to be segregated in the grain boundaries to play a role in strengthening the grain boundaries, and the rare earth elements are used as active elements to improve the oxidation resistance of the alloy and improve the surface stability.
Further, in the steel for a low-temperature pressure vessel according to the present invention, the microstructure thereof has Ti (C, N) particles and MgO and/or MgS particles.
The addition of Ti and Mg to the steel for low-temperature pressure vessels according to the invention promotes the formation of small amounts of Ti (C, N) and MgO and/or MgS particles in the alloy during cooling and solidification. The particles are beneficial to refining and stabilizing austenite grains, so that the defect that the steel for the low-temperature pressure container forms cracks on the surfaces of continuous casting billets or hot rolled plates is avoided, and the low-temperature impact toughness of the material can be improved.
Further, in the steel for a low temperature pressure vessel according to the present invention, the Ti (C, N) particles, MgO and/or MgS particles have a diameter of about 0.1 to 8 μm.
Further, in the steel for a low-temperature pressure vessel according to the present invention, the number of Ti (C, N) particles and MgO and/or MgS particles is 5 to 25/mm in a cross section of the steel for a low-temperature pressure vessel2。
Further, in the steel for a low-temperature pressure vessel, the mass percentage of Ti is 0.1-0.2%.
Further, in the steel for a low-temperature pressure vessel, the mass percentage of Mg is 0.001-0.003%.
Furthermore, in the steel for the low-temperature pressure container, the tensile strength is more than or equal to 850MPa, the yield strength is more than or equal to 625MPa, the elongation is more than or equal to 25 percent, and the impact toughness at-196 ℃ is more than or equal to 150J.
Accordingly, another object of the present invention is to provide a method for manufacturing the steel for a low temperature pressure vessel as described above, comprising the steps of:
(1) smelting, namely smelting in a converter, and then refining by L F + RH;
(2) continuous casting;
(3) hot rolling;
(4) quenching heat treatment;
(5) and (6) tempering.
In the manufacturing method, a small amount of ferrotitanium is added to add Ti and nickel-magnesium alloy is added to add Mg) at the final stage of RH refining, after the mass percentages of all elements in the steel are further controlled to meet the range defined by the invention, argon blowing soft stirring is carried out, and the flow of argon is controlled to be 5-8 liters/minute.
Further, the manufacturing method according to the present invention further includes a thinning step before the hot rolling step.
Further, in the manufacturing method of the present invention, in the step (2), the pulling rate is controlled to be 0.9 to 1.2 m/min.
Further, in the manufacturing method of the invention, in the step (2), a crystallizer is adopted for electromagnetic stirring during continuous casting, the current is controlled to be 500-1000A, and the frequency is 2.5-3.5 Hz, so that the isometric crystal proportion of the continuously cast slab is more than or equal to 40%.
Further, in the manufacturing method of the present invention, the step (3) includes rough rolling and finish rolling, wherein the rough rolling temperature is controlled to 1150 to 1250 ℃, and the finish rolling temperature is controlled to 1050 to 1150 ℃.
Further, in the production method of the present invention, in the step (3), the total rolling reduction is controlled to be 60 to 95%.
Further, in the manufacturing method of the invention, in the step (4), the quenching heat treatment temperature is 750-850 ℃, the heat preservation time is 60-90min, and water cooling is performed when the steel is taken out of the furnace.
Further, in the manufacturing method of the invention, in the step (5), the tempering temperature is 550-650 ℃, the heat preservation time is 40-120min, and the air cooling is carried out after the furnace is taken out. The parameter setting of the scheme is favorable for improving the room-temperature mechanical property and the low-temperature impact toughness of the steel, so that a hot-rolled product with comprehensive performance meeting the production requirement is obtained.
The steel for the low-temperature pressure container is designed by adding the microalloy, excessive expensive elements such as Ni are not required to be added, and the low-content total oxygen is controlled by adding a proper amount of Nb, Ti and Mg, so that the steel for the low-temperature pressure container has high strength, good formability and low-temperature impact toughness, and the cost of the steel material is lower compared with that of the prior art.
Detailed Description
The steel for a low-temperature pressure vessel and the method for manufacturing the same according to the present invention will be further explained and illustrated with reference to specific examples, but the explanation and illustration are not intended to unduly limit the technical aspects of the present invention.
Examples 1 to 6 and comparative examples 1 to 3
The steels for low-temperature pressure vessels of examples 1 to 6 were prepared by the following steps:
(1) smelting, namely smelting in a converter, then refining by L F + RH, and controlling the mass percentage of each chemical element as shown in Table 3;
(2) continuous casting: controlling the pulling speed to be 0.9-1.2 m/min, electromagnetically stirring by using a crystallizer during continuous casting, controlling the current to be 500A and the frequency to be 2.5-3.5 Hz, so that the isometric crystal ratio of the continuously cast plate blank is more than or equal to 40 percent;
(3) hot rolling: the method comprises rough rolling and finish rolling, wherein the rough rolling temperature is controlled to be 1150-1250 ℃, the finish rolling temperature is controlled to be 1050-1150 ℃, and the total pressure efficiency is controlled to be 60-95%;
(4) quenching heat treatment: the temperature is 750-850 ℃, the heat preservation time is 60-90min, and the product is taken out of the furnace and cooled by water;
(5) tempering treatment: the temperature is 550-650 ℃, the heat preservation time is 40-120min, and the product is discharged from the furnace and cooled in air.
The steels for low-temperature pressure vessels of examples 1 to 6 further had a thinning step before the hot rolling step. The conventional steels of comparative examples 1 to 3 were prepared using the prior art.
Table 3 shows the mass percentages of the chemical elements and the microstructures of the steels for cryogenic pressure vessels of examples 1 to 6 and the conventional steels of comparative examples 1 to 3.
TABLE 3 (wt%, balance Fe and unavoidable impurity elements other than O, P and S)
Figure BDA0001387272940000071
Table 4 lists the specific process parameters of the manufacturing method of each example.
Table 4.
Figure BDA0001387272940000072
Figure BDA0001387272940000081
For the above examples 1-6 of this documentThe microstructure of the steel for the low-temperature pressure container is observed, and the microstructure of each embodiment is an austenite structure from the solidification of a continuous casting plate blank to the room temperature, and the microstructure of each embodiment is low-carbon tempered martensite after hot rolling and Quenching and Tempering (QT) heat treatment, wherein the quenching treatment can obtain martensite with fine crystal grains, the tempering treatment can convert the martensite structure into ferrite and fine precipitated carbide, and a small amount of dispersed austenite can be obtained, and the microstructure can greatly improve the toughness of a base material, and is particularly suitable for manufacturing low-temperature-resistant and pressure-bearing parts. Wherein the microstructures of the examples have Ti (C, N) grains and CaO and/or CaS grains, the Ti (C, N) grains, CaO and/or CaS grains have a diameter of about 0.1 to 8 μm, and the number of the Ti (C, N) grains and CaO and/or CaS grains is 5 to 25/mm in a cross section of the steel for the low-temperature pressure vessel2。
Further, the steels for cryogenic pressure vessels of examples 1 to 6 and the conventional steels of comparative examples 1 to 3 were sampled, and various performance tests were conducted, and the results obtained by the tests are shown in Table 5.
Table 5 shows the results of the data measured after the steels for cryogenic pressure vessels of examples 1 to 6 and the conventional steels of comparative examples 1 to 3 were tested.
Table 5.
Numbering Yield strength Rel(MPa) Tensile strength Rm(MPa) Elongation (%) Impact toughness at-196 ℃ (J)
Example 1 635 863 27 167
Example 2 630 858 26 157
Example 3 625 857 25 163
Example 4 640 862 28 150
Example 5 638 868 29 169
Example 6 642 858 27 155
Comparative example 1 576 695 20 108
Comparative example 2 584 734 18 105
Comparative example 3 593 721 19 107
As can be seen from Table 5, the yield strength, tensile strength, elongation and impact toughness at-196 ℃ of each example are significantly higher than the yield strength, tensile strength, elongation and impact toughness at-196 ℃ of each comparative example, which shows that the mechanical properties and low-temperature impact toughness of each example are high. In addition, the tensile strength of each example is not less than 850MPa, the yield strength is not less than 625MPa, the elongation is not less than 25%, and the impact toughness at-196 ℃ is not less than 150J.
It should be noted that the prior art in the protection scope of the present invention is not limited to the examples given in the present application, and all the prior art which is not inconsistent with the technical scheme of the present invention, including but not limited to the prior patent documents, the prior publications and the like, can be included in the protection scope of the present invention.
In addition, the combination of the features in the present application is not limited to the combination described in the claims of the present application or the combination described in the embodiments, and all the features described in the present application may be freely combined or combined in any manner unless contradictory to each other.
It should be noted that the above-mentioned embodiments are only specific examples of the present invention, and obviously, the present invention is not limited to the above-mentioned embodiments, and many similar variations exist. All modifications which would occur to one skilled in the art and which are, therefore, directly derived or suggested from the disclosure herein are deemed to be within the scope of the present invention.

Claims (13)

1. The steel for the low-temperature pressure container is characterized by comprising the following chemical elements in percentage by mass:
0.02-0.08% of C, 0.10-0.35% of Si, 0.3-0.8% of Mn, 7.0-12.0% of Ni, less than or equal to 0.005% of N, 0.015-0.05% of Al, 0.1-0.3% of Nb, 0.1-0.3% of Ti and 0.001-0.005% of Mg; the balance being Fe and other unavoidable impurities;
the microstructure of the steel for the low-temperature pressure container is an austenite structure from the beginning of solidification to the room temperature state; wherein the microstructure of the steel for cryogenic pressure vessels has Ti (C, N) particles and MgO and/or MgS particles, the Ti (C, N) particles, MgO and/or MgS particles having a diameter of 0.1-8 μm; in the section of the steel for the low-temperature pressure vessel, the number of Ti (C, N) particles and MgO and/or MgS particles is 5-25/mm2。
2. The steel for low-temperature pressure vessels as claimed in claim 1, wherein the chemical elements further comprise at least one of Ce, Hf, L a, Re, Sc and Y, and the total mass percentage of these elements is 1% or less.
3. The steel for a low-temperature pressure vessel as claimed in claim 1, wherein the Ti is contained in an amount of 0.1 to 0.2% by mass.
4. The steel for a low-temperature pressure vessel as set forth in claim 1, wherein Mg is contained in an amount of 0.001 to 0.003% by mass.
5. The steel for a low-temperature pressure vessel according to claim 1, wherein the steel has a tensile strength of 850MPa or more, a yield strength of 625MPa or more, an elongation of 25% or more, and an impact toughness of 150J or more at-196 ℃.
6. The method for manufacturing steel for a cryogenic pressure vessel according to any one of claims 1 to 5, comprising the steps of:
(1) smelting, namely smelting in a converter, and then refining by L F + RH;
(2) continuous casting;
(3) hot rolling;
(4) quenching heat treatment;
(5) and (6) tempering.
7. The manufacturing method according to claim 6, further comprising a thinning step before the hot rolling step.
8. The method according to claim 6 or 7, wherein in the step (2), the pulling rate is controlled to be 0.9 to 1.2 m/min.
9. The manufacturing method according to claim 6 or 7, wherein in the step (2), the mold is used for electromagnetic stirring during continuous casting, the current is controlled to be 500-1000A, and the frequency is controlled to be 2.5-3.5 Hz, so that the equiaxed crystal ratio of the continuously cast slab is not less than 40%.
10. The manufacturing method according to claim 6 or 7, wherein the step (3) includes rough rolling and finish rolling, wherein the rough rolling temperature is controlled to 1150 to 1250 ℃ and the finish rolling temperature is controlled to 1050 to 1150 ℃.
11. The production method according to claim 6 or 7, wherein in the step (3), the total rolling reduction is controlled to be 60 to 95%.
12. The method according to claim 6 or 7, wherein in the step (4), the quenching heat treatment temperature is 750 to 850 ℃, the holding time is 60 to 90min, and water cooling is performed during discharging.
13. The production method according to claim 6 or 7, wherein in the step (5), the tempering temperature is 550 to 650 ℃, the holding time is 40 to 120min, and the air cooling is performed after the product is taken out of the furnace.
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PCT/CN2018/101858 WO2019037749A1 (en) 2017-08-23 2018-08-23 Steel for use in low-temperature pressurized vessel and manufacturing method therefor
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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004360064A (en) * 2003-05-15 2004-12-24 Sumitomo Metal Ind Ltd Steel material superior in beach weather resistance, and structure using it
JP2005097682A (en) * 2003-09-25 2005-04-14 Nisshin Steel Co Ltd Steel, steel sheet and stock belt for continuously variable transmission belt, continuously variable transmission belt, and production method therefor
CN103764859A (en) * 2011-09-28 2014-04-30 新日铁住金株式会社 Nickel steel plate and manufacturing process therefor

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004360064A (en) * 2003-05-15 2004-12-24 Sumitomo Metal Ind Ltd Steel material superior in beach weather resistance, and structure using it
JP2005097682A (en) * 2003-09-25 2005-04-14 Nisshin Steel Co Ltd Steel, steel sheet and stock belt for continuously variable transmission belt, continuously variable transmission belt, and production method therefor
CN103764859A (en) * 2011-09-28 2014-04-30 新日铁住金株式会社 Nickel steel plate and manufacturing process therefor

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