KR102364473B1 - Steel for low-temperature pressure vessel and manufacturing method thereof - Google Patents

Abstract

Steel for low temperature pressure vessel, the mass percentage of chemical elements is C 0.02-0.08%, Si 0.10-0.35%, Mn 0.3-0.8%, Ni 7.0-12.0%, N≤0.005%, Al 0.015-0.05%, Nb 0.1 -0.3%, Ca and/or Mg 0.001-0.005%, optionally selected V and/or Ti 0.1-0.3%; the balance being Fe and other unavoidable impurities. The manufacturing method of the low-temperature pressure vessel steel includes: (1) smelting: LF+RH refining after converter refining; (2) continuous casting; (3) hot rolling; (4) quenching heat treatment; (5) tempering treatment; includes steps. The low-temperature pressure vessel steel has high low-temperature impact toughness.

Description

Steel for low-temperature pressure vessel and manufacturing method thereof

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to steel and a method for producing it, and more particularly to a steel containing nickel for use in low-temperature pressure vessels and a method for producing the same.

9% Ni steel refers to low-carbon steel containing about 9% of Ni element. In 1952, the first 9% Ni steel storage tanks were put into service in the United States. Japan built the first natural gas cold storage tank in Japan in 1969, and the maximum capacity of the natural gas cold storage tank currently reaches 20Хl0 ⁴ m ³ . As natural gas confirmed reserves increase, the Chinese government is paying more and more attention to the development and utilization of natural gas, and the design and construction of cold storage equipment. In the 1980s, a 9% Ni steel ethylene spherical tank was successfully constructed for the first time in Daekyung Ethylene Corporation. In 2004, Guangdong Natural Gas Corporation, China's first large-scale low-temperature liquefied natural gas project, started construction, and the capacity of a single tank reaches 16Х10 ⁴ m ³ . So far, the history of applying 9%Ni steel to natural gas facilities is over 60 years. Because 9% Ni steel has excellent low-temperature toughness and welding performance, it has become a widely used type of steel in the field of low-temperature equipment internationally.

The low-temperature mechanical properties of 9% Ni steels are mainly determined by the chemical composition, in particular the content of the elements Ni and C. Also, the toughness of steel is determined by the purity and microstructure of the steel.

The ironmaking process of continuous casting is used for the production of 9% Ni steel, and the metallurgical treatment, vacuum degassing process and high purity during the casting process play a very important role in improving the low-temperature toughness of the steel. Since the presence of impurity elements such as P and S degrades the low-temperature toughness of steel, the content of impurity elements such as P and S must be strictly controlled to a low level.

Japan included 9% Ni steel in its JIS standard in 1977. In the same year, the United States also included 9% Ni steel in its ASME and ASTM standards. The codes, chemical compositions and mechanical properties of 9% Ni steels for each major industrial country are shown in Tables 1 and 2.

Chemical composition (wt%) of typical steel grades relevant in the prior art nation Standard C Si Mn S P Ni Al USA ASTM A 553 ≤0.13 0.15-0.30 ≤0.9 ≤0.04 ≤0.035 8.5-9.5 ≥0.015 USA ASTM A 553 ≤0.13 0.15-0.45 ≤0.98 ≤0.04 ≤0.035 8.4-9.6 ≥0.015 Germany VDEh680X8Ni9 ≤0.1 0.10-0.35 0.3-0.8 ≤0.035 ≤0.035 8.5-9.5 ≥0.015 Japan JIS G 3127SL9N 590 ≤0.12 ≤0.30 ≤0.90 ≤0.025 ≤0.025 8.5-9.5 ≥0.015 UK EN10028-4 ≤0.10 ≤0.35 0.3-0.8 ≤0.005 ≤0.015 8.5-9.5 ≥0.015 China GB3531-2014 ≤0.08 0.15-0.35 0.3-0.8 ≤0.004 ≤0.008 8.5-10.0 ≥0.015

Mechanical properties of typical steel grades relevant in the prior art nation yield strength
Rel(MPa) tensile strength
Rm(MPa) Elongation (%) Impact toughness (J) at -196°C USA ≥585 690-825 20 ≥100 USA ≥585 690-825 18 ≥100 Germany 490 637-833 18 ≥100 Japan ≥590 690-830 20 ≥100 UK ≥590 690-830 20 ≥100 China ≥575 680-820 20 ≥100

As can be seen from Tables 1 and 2, the prior art steel for low-temperature pressure vessels does not meet the increasing demands of use and manufacturing. In view of this, a steel for a low-temperature pressure vessel with further improved mechanical properties and low-temperature impact toughness compared to the prior art and a lower production cost is expected.

The present invention does not require the addition of large amounts of expensive elements such as Ni through the design of adding microalloys, only appropriate amounts of Nb, Ca and/or Mg elements and optionally selected V and/or Ti are added and total oxygen An object of the present invention is to provide a steel for a low-temperature pressure vessel having high strength, good forming performance and low-temperature impact toughness by controlling the content to a low level, and the cost of steel material being lower than that of the prior art.

According to the above object, the present invention provides a steel for a low-temperature pressure vessel, wherein the mass percentage of the chemical element of the steel for a low-temperature pressure vessel is C 0.02-0.08%, Si 0.10-0.35%, Mn 0.3-0.8%, Ni 7.0-12.0%, N≤0.005%, Al 0.015-0.05%, Nb 0.1-0.3%, Mg 0-0.005%, Ca 0-0.005%, V 0-0.3% and Ti 0-0.3%; The remainder is Fe and other unavoidable impurities; The sum of the mass percentages of Ca and Mg is 0.001-0.005%.

In some embodiments, the steel for low temperature pressure vessel of the present invention contains only at least one or two of Ca and Mg and no V and Ti. In these embodiments, the mass percentage of the chemical elements of the steel for low temperature pressure vessel of the present invention is C 0.02-0.08%, Si 0.10-0.35%, Mn 0.3-0.8%, Ni 7.0-12.0%, N≤0.005%, Al 0.015 -0.05%, Nb 0.1-0.3%, Ca and/or Mg 0.001-0.005%; The remainder is Fe and other unavoidable impurities.

In some embodiments, the steel for low-temperature pressure vessel of the present invention further contains at least one or two of V and Ti, and the sum of the mass percentages of V and Ti is in the range of 0.1-0.3%. Therefore, in these embodiments, the mass percentage of the chemical elements of the steel for low temperature pressure vessel of the present invention is C 0.02-0.08%, Si 0.10-0.35%, Mn 0.3-0.8%, Ni 7.0-12.0%, N≤0.005%, Al 0.015-0.05%, Nb 0.1-0.3%, V and/or Ti 0.1-0.3%, Ca and/or Mg 0.001-0.005%; The remainder is Fe and other unavoidable impurities.

In some embodiments, the steel for low temperature pressure vessel of the present invention contains V and Ca, and the mass percentage of chemical elements is 0.02-0.08% C, 0.10-0.35% Si, 0.3-0.8% Mn, 7.0-12.0% Ni , N≤0.005%, Al 0.015-0.05%, Nb 0.1-0.3%, V 0.1-0.3%, Ca 0.001-0.005%; The remainder is Fe and other unavoidable impurities. In some embodiments, the mass percentages of the chemical elements of the low temperature pressure vessel steel are: C 0.02-0.06%, Si 0.10-0.35%, Mn 0.3-0.8%, Ni 7.0-12.0%, N≤0.005%, Al 0.015-0.05 %, Nb 0.1-0.3%, V 0.1-0.3%, Ca 0.001-0.005%; The remainder is Fe and other unavoidable impurities.

In some embodiments, the steel for low temperature pressure vessel of the present invention contains Ti and Mg, and the mass percentage of chemical elements is 0.02-0.08% C, 0.10-0.35% Si, 0.3-0.8% Mn, 7.0-12.0% Ni. , N≤0.005%, Al 0.015-0.05%, Nb 0.1-0.3%, Ti 0.1-0.3%, Mg 0.001-0.005%; The remainder is Fe and other unavoidable impurities.

In some embodiments, the steel for low temperature pressure vessel of the present invention contains only Mg and contains no Ca, Ti and V, and the mass percentages of chemical elements are C 0.02-0.08%, Si 0.10-0.35%, Mn 0.3- 0.8%, Ni 7.0-12.0%, N≤0.005%, Al 0.015-0.05%, Nb 0.1-0.3%, Mg 0.001-0.005% (preferably 0.001-0.003%); The remainder is Fe and other unavoidable impurities.

Compared with the prior art, the steel for low-temperature pressure vessel of the present invention is advantageous for increasing strength and improving impact toughness by adding an appropriate amount of Nb to form Nb(C,N); In addition, the addition of Ca and/or Mg and optionally V and/or Ti serves to significantly improve the low-temperature impact toughness of the steel and at the same time improve the strength of the steel.

In addition, in the present technical solution, the evolution of the microstructure of the steel for the low-temperature pressure vessel is as follows. That is, from the time the continuous casting slab begins to solidify and reaches a room temperature state, all are austenitic structures. After hot rolling, the main structures of quenching and tempering (QT) heat treatment are all low-carbon tempered martensite. Here, martensite having fine grains is obtained through the quenching treatment, and the martensite structure is converted into ferrite and fine precipitation carbide through the subsequent tempering treatment, while at the same time a small amount of dispersed austenite can be obtained. It can be significantly improved and is particularly suitable for the manufacture of low-temperature and pressure-resistant parts.

The design principle of each chemical element of the steel for low-temperature pressure vessel of the present invention is as follows.

C: In general, the mass percentage of C mainly affects the precipitation amount of carbides and the precipitation temperature range. In the steel for low-temperature pressure vessel of the present invention, carbon has a certain strengthening action, and controlling the mass percentage of C to a relatively low level is advantageous for improving the impact toughness of the steel. Also, if the mass percentage of carbon is too high, the corrosion resistance of the material may be reduced. To balance mechanical properties and impact toughness, the mass percentage of C can be controlled to 0.02-0.08%. In some embodiments, the mass percentage of C is controlled between 0.02-0.06%.

Si: Si can improve the strength of steel, but is disadvantageous to the formability and toughness of the steel. In the steel for low-temperature pressure vessel of the present invention, the mass percentage of Si is controlled to 0.10-0.35%, preferably 0.10-0.30%.

Mn: Mn is an austenitic element, which can suppress the harmful effect of S in the nickel-based corrosion-resistant alloy and improve the thermoplasticity. However, if the mass percentage of Mn is too high, it is disadvantageous to secure corrosion resistance. Therefore, in the steel for low-temperature pressure vessel of the present invention, the mass percentage of M is limited to 0.3 to 0.8%, preferably 0.35-0.7% in consideration of mechanical properties and corrosion resistance.

Ni: Ni is a major element of the steel for low-temperature pressure vessels of the present invention, and has excellent austenite phase stability and can improve mechanical properties and impact toughness of the steel for low-temperature pressure vessels of the present invention. As Ni increases, the tensile strength at high temperature gradually increases, which means that when the mass percentage of Ni is low, most of it is dissolved in austenite as a solid, thereby expanding the austenite phase region and increasing the recrystallization temperature, thereby reducing the mechanical properties of the alloy. because it has improved. Accordingly, the mass percentage of Ni in the steel for low-temperature pressure vessel of the present invention is limited to 7.0-12.0%, preferably 7.5 to 10.5%.

N: N is a stable austenitic element. Controlling the mass percentage of N to a low level is advantageous for improving the impact toughness of steel for low-temperature pressure vessels. In addition, when the mass percentage of nitrogen is high, not only the toughness and malleability of the steel are reduced, but also the thermal workability of the steel is reduced. Therefore, the mass percentage of N in the steel for low temperature pressure vessel of the present invention is limited to N≤0.005%.

Al: In the technical solution of the present invention, by controlling the oxygen content of steel mainly through Al, the dislocation behavior is affected to strengthen the alloy. Increasing the mass percentage of Al can significantly increase the melting temperature and creep strength, but if the mass percentage of Al is too high, it can reduce the plasticity of the steel. In addition, the addition of Al improves the elongation and deformation properties of the steel, which is advantageous for improving the workability of the steel. However, an Al content in which the mass percentage exceeds 0.05% deteriorates the impact toughness of the steel. In consideration of the above, the mass percentage of Al in the steel for low-temperature pressure vessel of the present invention is limited to 0.015-0.05%, preferably 0.02-0.04%.

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. In addition, Nb is a very strong carbonitride forming element, and since it combines with carbon and nitrogen to form Nb(C,N), it is advantageous for improving strength and impact toughness. At the same time, carbon and nitrogen have a certain strengthening action, and Nb in the steel forms Nb(C,N) to strengthen the austenite phase matrix, refine the austenite crystal grains, and strengthen the boundaries between the austenite grains, It is advantageous for improving the low-temperature impact toughness of steel for low-temperature pressure vessels. Therefore, the mass percentage of Nb in the steel for low-temperature pressure vessel of the present invention is limited to 0.1-0.3%, preferably 0.1-0.2%.

Mg: Magnesium as a trace element separates and reduces grain boundary energy and phase boundary energy at grain boundaries, improves and refines the shape of grain carbides and other grain boundary precipitation phases such as blockage and spheroidization of carbides, effectively suppresses grain boundary sliding, and reduces grain boundaries Reduce stress stress and eliminate notch sensitivity. In addition, MgO and MgS, which are compounds of high melting point, which are harmful impurities such as magnesium and sulfur, are formed, and the grain boundaries are purified to significantly reduce the concentration of impurity elements such as S, O and P at the grain boundaries and reduce the harmfulness of the impurity elements. In the solidification process, MgO and MgS in the steel can be used as nucleation particles for refining grains. The trace element magnesium improves plasticity, improves high-temperature tensile plasticity, and increases impact toughness and fatigue strength.

Ca: Calcium can change the composition, quantity, and shape of non-metallic inclusions in the steel. In addition, adding calcium can refine the grains of steel, deoxygenation and desulfurization, and the formed CaO and CaS are used as nucleation particles to solidify The structure can be refined. In addition, it improves the corrosion resistance, wear resistance, high temperature resistance and low temperature resistance of steel, improves plasticity, impact toughness, fatigue strength and welding performance of steel, and improves heat cracking resistance, hydrogen-induced cracking resistance and lamellar tear resistance.

The steel for low-temperature pressure vessel of the present invention contains any one or two of Ca and Mg, and the Ca content is 0-0.005%, for example 0.001-0.005%; The content of Mg is 0-0.005%, for example 0.001-0.005%; The prerequisite is that the sum of Ca+Mg content should be in the range of 0.001-0.005%. In some embodiments, the steel for low temperature pressure vessel of the present invention contains only Mg, and the content is in the range of 0.001-0.005%, preferably in the range of 0.001-0.003%.

V: V can refine grains and improve strength and toughness. In order to obtain fine martensite after quenching, adding vanadium is a relatively effective method. Vanadium is an element that strongly forms carbides and forms stable VC due to its extremely strong bonding to carbon. Whether precipitating in the tempering process or forming particles of VC in another step, the particles are all fine and dispersed. When niobium-vanadium is added in combination, the strength is higher than when Nb alone is added. At the same time, it is advantageous for improving strength and toughness by further refining the austenite grains to further refine the ferrite grains after cooling.

Ti: Ti has a solid solution strengthening and precipitation strengthening action for steel, and has a strong bonding force with O to reduce the oxygen content of the steel. In addition, Ti may be combined with C and N to form Ti(C,N) and refine the solidified structure. In alloys with high Ni content, especially under the joint action of Nb and Al, the addition of Ti can form Ni3(Al,Ti,Nb) to improve the strength and toughness of steel.

The steel for low temperature pressure vessel of the present invention may contain any one or both of V and Ti, and the content of V may be 0-0.3%, for example 0.1-0.3%; The content of Ti may be 0-0.3%, for example, 0.1-0.3%. In some embodiments, when V and/or Ti is contained, the sum of the contents of V+Ti is limited to 0.1-0.3%.

It should be noted that, in the technical scheme of the present invention, unavoidable impurity elements include O, P and S. In the technical scheme of the present invention, O is mainly present as oxide inclusions, and the higher the total oxygen content, the more the inclusions are present. Reducing the total oxygen content is advantageous for improving the overall performance of the material. Therefore, the mass percentage of the unavoidable impurities in the steel for low-temperature pressure vessel is controlled to be total oxygen ≤ 0.001%, P ≤ 0.010%, and S ≤ 0.005%.

Further, in the steel for low-temperature pressure vessel of the present invention, the chemical element also includes a rare earth element, and the mass percentage ≤ 1%, for example, 0.1-1%. In the present invention, the rare earth elements include Ce, Hf, La, Re, Sc and Y. At least one of Ce, Hf, La, Re, Sc, and Y may be added to the steel for low-temperature pressure vessel of the present invention, and the added rare-earth element should have a total mass percentage ≤ 1%.

In the technical solution of the present invention, the rare earth element has a deoxidation and desulfurization action as a purifying agent, thereby reducing the harmful effects of oxygen and sulfur on grain boundaries. In addition, the rare earth element is separated at the grain boundary as a fine alloy element, and serves to strengthen the grain boundary. In addition, the rare earth element as an active element improves the oxidation resistance of the alloy and improves the surface stability.

In addition, in the steel for low-temperature pressure vessel of the present invention, the microstructure contains (Nb) CN particles, MgO and/or MgS particles and/or CaO and/or CaS particles, and optionally V(C,N) particles and / or containing Ti(C,N) particles.

When V and Ti or a combination thereof and Mg and Ca or a combination thereof are added to the steel for low-temperature pressure vessel of the present invention, a small amount of V(C,N) and/or Ti(C,N) is added to the alloy during cooling and solidification ) and CaO and/or MgO and/or CaS particles and/or MgS particles. Since the particles are advantageous for refining and stabilizing the austenite particles, it is possible to prevent crack defects from occurring on the hot-rolled sheet surface of a continuous casting slab or steel for a low-temperature pressure vessel and improve the low-temperature impact toughness of the material.

Further, in the steel for low-temperature pressure vessel of the present invention, when V(C,N) particles are contained, the diameter of these particles is about 0.2-5 μm, and when CaO and/or CaS particles are contained, the diameter of these particles is about 0.2-5 μm, when Ti(C,N) particles are contained, the diameter of these particles is about 0.1-8 μm, and when MgO and/or MgS particles are contained, the diameter of these particles is about 0.1-8 μm am.

In addition, in the steel for low-temperature pressure vessel of the present invention, when the particles are contained, the quantity of V(C,N) particles in the cross section of the steel for low-temperature pressure vessel is 5 to 20 pieces/mm ² , and CaO and/or The quantity of CaS particles is 5-20 pieces/mm ² , the quantity of Ti (C,N) particles is 5-25 pieces/mm ² , and the quantity of MgO and/or MgS particles is 5-25 pieces/mm ² . When only Mg and/or Ca is contained and V and/or Ti is not contained, the quantity of MgO and/or MgS particles and/or CaO and/or CaS is 15 to 55 pieces/mm ² .

Further, in the steel for low-temperature pressure vessel of the present invention, when it contains only V, its mass percentage content is 0.1-0.2%; When containing only Ti, its mass percentage content is 0.1-0.2%; Alternatively, when V and Ti are contained simultaneously, the sum of the mass percentage contents of both is 0.1-0.2%.

Further, in the steel for low-temperature pressure vessel of the present invention, when it contains only Ca, its mass percentage content is 0.001-0.003%; or, if it contains only Mg, its mass percentage content is 0.001-0.003%; Alternatively, when Ca and Mg are contained simultaneously, the sum of the mass percentage contents of both is 0.001-0.003%.

Accordingly, in some embodiments, the mass percentages of the chemical elements of the steel for low temperature pressure vessels of the present invention are: In other words:

C: 0.02-0.08%, preferably 0.02-0.06%;

Si: 0.10-0.35%, preferably 0.1-0.3%;

Mn: 0.3-0.8%, preferably 0.35-0.7%;

Ni: 7.0-12.0%, preferably 7.5-10.5%;

N: ≤0.005%;

Al: 0.015-0.05%, preferably 0.02-0.04%;

Nb: 0.1-0.3%, preferably 0.1-0.2%;

Mg: 0.001-0.005%, preferably 0.001-0.003%, or Ca: 0.001-0.005%, preferably 0.001-0.003%, or Mg+Ca: 0.001-0.005%, preferably 0.001-0.003%;

V is optionally selected from 0.1-0.3%, preferably 0.1-0.2%;

Ti is optionally selected from 0.1-0.3%, preferably 0.1-0.2%; and,

Rare earth element: ≤1%;

The remainder is Fe and other unavoidable impurities.

In some embodiments, the mass percentages of the chemical elements of the steel for low temperature pressure vessels of the present invention are: In other words:

C: 0.02-0.06%;

Si: 0.1-0.3%;

Mn: 0.35-0.7%;

Ni: 7.5-10.5%;

N: ≤0.005%;

Al: 0.02-0.04%;

Nb: 0.1-0.2%;

Mg: 0.001-0.003%, or Ca:0.001-0.003%, or Mg+Ca:0.001-0.003%;

V is optionally selected from 0.1-0.3%, preferably 0.1-0.2%;

Ti is optionally selected from 0.1-0.3%, preferably 0.1-0.2%; and,

Rare earth element: ≤1%;

The remainder is Fe and other unavoidable impurities.

Further, in the steel for low-temperature pressure vessel of the present invention, tensile strength≥850MPa, yield strength≥625MPa, elongation≥25%, impact toughness≥150J at -196°C. In some embodiments, in the steel for low temperature pressure vessel of the present invention, the tensile strength is 850-870 MPa, the yield strength is 625-650 MPa, the elongation is 25-30%, and the impact toughness at -196°C is 150-170J .

Another object of the present invention is to provide a method for manufacturing the steel for a low-temperature pressure vessel, the manufacturing method comprising the following steps. In other words:

(1)Smelting: After converter smelting, LF+RH refining;

(2) continuous casting;

(3) hot rolling;

(4) quenching heat treatment; and,

(5) Tempering treatment.

In the production method of the present invention, by adding a small amount of ferrovanadium and/or ferrotitanium in the final process of RH refining, adding V and/or Ti, adding Ca by adding a calcium wire, and adding a nickel-magnesium alloy After adding Mg and further controlling the mass percentage of each element in the steel according to the limited scope of the present invention, gentle stirring is performed using argon gas, and the flow rate of argon gas is controlled to 5-8 liters/min. .

Further, in the manufacturing method of the present invention, a polishing step is further included before the hot rolling step.

In addition, in the manufacturing method of the present invention, the withdrawal speed in step (2) is controlled to 0.9 ~ 1.2 m / min.

40%이 되도록, 전류는 500-1000A, 주파수는 2.5~3.5Hz로 제어한다.In addition, in the manufacturing method of the present invention, the electromagnetic stirrer of the crystallizer is used during continuous casting in step (2), and the ratio of equiaxed crystals of the slab after continuous casting

To be 40%, the current is 500-1000A, and the frequency is 2.5-3.5Hz.

In addition, in the manufacturing method of the present invention, the step (3) includes rough rolling and finish rolling, the rough rolling temperature is 1150 ~ 1250 ℃, the finish rolling temperature is controlled to 1050 ~ 1150 ℃.

In addition, in the manufacturing method of the present invention, the total rolling reduction in step (3) is controlled to be 60 to 95%, for example, 60 to 90%.

In addition, in the manufacturing method of the present invention, the quenching heat treatment temperature in step (4) is 750 ~ 850 ℃, the holding time is 60-90min, and proceeds with water cooling when tapping.

In addition, in the manufacturing method of the present invention, the tempering treatment temperature in step (5) is 550 ~ 650 ℃, the holding time is 40-120min, and proceeds with air cooling after tapping. Setting the parameters according to the above scheme is advantageous for improving the room temperature mechanical properties and low temperature impact toughness of the steel, so that a hot-rolled product whose overall performance can meet the production needs can be obtained.

The steel for low temperature pressure vessel of the present invention does not need to add large amounts of expensive elements such as Ni through the design of adding microalloys, only appropriate amounts of Nb, Ca and/or Mg elements and arbitrarily selected V and/or By adding Ti and controlling the total oxygen content to a low level, the steel for low-temperature pressure vessel has higher strength, good forming performance and low-temperature impact toughness, and the cost of steel material is lower than that of the prior art.

Hereinafter, the steel for low-temperature pressure vessel of the present invention and its manufacturing method will be further analyzed and described in conjunction with specific examples, but the above analysis and description are not intended to limit the technical solution of the present invention.

Examples 1-6 and Comparative Examples 1-3

The steel for low-temperature pressure vessel of Example 1-6 was manufactured through the following steps. In other words:

(1) Smelting: After converter smelting, LF+RH refining to control the mass percentage of each chemical element as shown in Table 3;

(2)Continuous Casting: Control the drawing speed to 0.9~1.2m/min, use the electromagnetic stirrer of the crystallizer during continuous casting, and the current is so that the equiaxed crystal ratio of the slab after continuous casting is ≥40% 500-1000A, frequency controlled by 2.5-3.5Hz;

(3) hot rolling: including rough rolling and finish rolling, the rough rolling temperature is 1150 to 1250 ° C, the finish rolling temperature is 1050 to 1150 ° C, and the total rolling reduction is controlled to be 60 to 90%;

(4) quenching heat treatment: the temperature is 750-850 ° C, the holding time is 60-90 min, and water cooling is carried out at the time of tapping;

(5) Tempering treatment: The temperature is 550~650℃, the holding time is 40-120min, and air cooling is performed after tapping.

The steel for low-temperature pressure vessel of Examples 1-6 further includes a polishing step before the hot rolling step. The comparative steels of Comparative Examples 1-3 were manufactured according to the prior art.

Table 3 shows the mass percentage of each chemical element of the steel for low-temperature pressure vessel of Example 1-6 and Comparative Example 1-3.

(wt%, the remainder is Fe and other unavoidable impurity elements other than O, P, and S) number C Si Mn Ni P S N Al Nb O V Ca rare earth elements Example 1 0.02 0.35 0.8 7 0.01 0.005 0.005 0.05 0.3 0.001 0.3 0.001 Ce: 0.1 Example 2 0.03 0.28 0.6 12 0.005 0.001 0.003 0.02 0.15 0.0008 0.2 0.003 - Example 3 0.05 0.15 0.4 8 0.006 0.002 0.004 0.04 0.22 0.0007 0.1 0.005 - Example 4 0.04 0.10 0.3 9 0.009 0.004 0.004 0.015 0.1 0.0009 0.18 0.002 La:
0.4 Example 5 0.08 0.19 0.5 11 0.007 0.003 0.005 0.03 0.18 0.001 0.22 0.003 - Example 6 0.06 0.22 0.7 10 0.008 0.005 0.003 0.025 0.26 0.0009 0.25 0.001 Y:
0.2 Comparative Example 1 0.07 0.18 0.5 9.5 0.004 0.002 0.005 0.018 0.23 0.0008 - - - Comparative Example 2 0.05 0.15 0.4 8 0.006 0.002 0.004 0.04 0.22 0.0007 - - - Comparative Example 3 0.06 0.22 0.7 10 0.007 0.004 0.004 0.035 0.28 0.0009 - - -

Table 4 shows specific process parameters of the manufacturing method of each Example.

Example number Step (2) Step (3) Step (4) Step (5) Withdrawal speed (m/min) Current (A) Frequency (Hz) Slab isometric ratio (%) Rough rolling temperature (℃) Finish rolling temperature)(℃ Total rolling reduction (%) Quenching heat treatment temperature (℃) Holding time (min) Tempering treatment (°C) holding time (min) One 0.9 500 3.5 40 1150 1050 75 750 70 650 50 2 1.0 620 3.0 50 1200 1100 60 810 60 610 40 3 1.1 880 2.5 42 1180 1080 90 850 80 550 100 4 0.95 750 3.0 49 1250 1150 85 780 90 575 90 5 1.2 1000 3.5 47 1220 1120 70 860 75 640 80 6 1.05 900 2.5 42 1230 1130 85 770 85 560 120

When observing the microstructure of the steel for low-temperature pressure vessel of Examples 1-6, the following facts can be found. That is, the microstructure of each embodiment of the present invention is an austenite structure from the start of the continuous casting slab solidification to a room temperature state, and after hot rolling, quenching and tempering (QT) heat treatment, the main structure of the present invention is all low-carbon It is tempered martensite, and through the quenching treatment, martensite having fine grains is obtained, and through the subsequent tempering treatment, the martensitic structure is converted into ferrite and fine precipitated carbide, while at the same time a small amount of dispersed austenite is obtained. This structure can significantly improve the toughness of the base material and is particularly suitable for manufacturing low-temperature and pressure-resistant parts. Here, the microstructure of each example has V(C,N) particles and CaO and/or CaS particles, and the diameter of the V(C,N) particles, CaO and/or CaS particles is about 0.2-5 μm, and the The quantity of V(C,N) particles and CaO and/or CaS particles in the cross section of the steel for low-temperature pressure vessel is 5-20 pieces/mm ² .

In addition, by collecting samples of the low-temperature pressure vessel steel of Example 1-6 and the comparative steel of Comparative Example 1-3, various performance tests were performed on the samples, and the test results are shown in Table 5.

number Yield strength R _el (MPa) Tensile strength R _m (MPa) Elongation (%) Impact toughness (J) at -196°C Example 1 625 854 26 153 Example 2 632 850 25 165 Example 3 629 862 26 158 Example 4 628 858 27 161 Example 5 626 865 26 156 Example 6 627 853 28 157 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°C of each Example of the present invention are all significantly higher than the yield strength, tensile strength, elongation and impact toughness at -196°C of each comparative example. high, which explains the high mechanical properties and low temperature impact toughness of each embodiment of the present invention. In addition, each Example has tensile strength≥850 MPa, yield strength≥625 MPa, elongation≥25%, and impact toughness≥150J at -196°C.

Example 7-12

The steel for low-temperature pressure vessel of Examples 7-12 was manufactured through the following steps. That is: (1) smelting: after converter smelting, LF+RH refining to control the mass percentage of each chemical element as shown in Table 3;

40%이 되도록, 전류는 500A, 주파수는 2.5~3.5Hz로 제어하며;(2)Continuous Casting: Controlling the drawing speed to 0.9~1.2m/min, using the electromagnetic stirrer of the crystallizer during continuous casting, and the ratio of equiaxed crystals of the slab after continuous casting

To be 40%, the current is 500A and the frequency is controlled to 2.5~3.5Hz;

(3) hot rolling: including rough rolling and finish rolling, the rough rolling temperature is 1150 to 1250 ° C, the finish rolling temperature is 1050 to 1150 ° C, and the total rolling reduction is controlled to be 60 to 90%;

(4) quenching heat treatment: the temperature is 750~850℃, the holding time is 60-90min, and water cooling is carried out at the time of tapping;

(5) Tempering treatment: The temperature is 550~650℃, the holding time is 40-120min, and air cooling is performed after tapping.

The steel for low-temperature pressure vessel of Examples 7-12 further includes a polishing step before the hot rolling step.

Table 6 shows the mass percentage of each chemical element of the steel for low-temperature pressure vessel of Examples 7-12.

(wt%, the remainder is Fe and other unavoidable impurity elements other than O, P, and S) number C Si Mn Ni P S N Al Nb O Ti Mg rare earth elements Example 7 0.04 0.10 0.5 11.0 0.008 0.004 0.002 0.015 0.10 0.0009 0.2 0.003 Ce:0.4 Example 8 0.08 0.30 0.3 9.0 0.003 0.003 0.003 0.03 0.13 0.0007 0.1 0.002 - Example 9 0.06 0.22 0.7 10.0 0.007 0.004 0.004 0.035 0.28 0.0009 0.3 0.001 Hf:0.5 Example 10 0.02 0.35 0.8 7.0 0.009 0.005 0.005 0.05 0.2 0.0008 0.1 0.002 Ce,La:0.7 Example 11 0.05 0.28 0.4 12.0 0.006 0.002 0.004 0.04 0.3 0.0010 0.2 0.001 - Example 12 0.03 0.18 0.6 8.0 0.004 0.005 0.003 0.025 0.18 0.0007 0.3 0.003 Se:0.3

Table 7 shows specific process parameters of the manufacturing method of each Example.

Example number Step (2) Step (3) Step (4) Step (5) Withdrawal speed (m/min) Current (A) Frequency (Hz) Slab isometric ratio (%) Rough rolling temperature (℃) Finishing rolling temperature (℃) Total rolling reduction (%) Quenching heat treatment (℃) Holding time (min) Tempering treatment (°C) Holding time (min) 7 0.9 500 3.5 40 1150 1050 65 750 90 650 40 8 1.0 600 3.0 45 1200 1100 60 800 80 600 50 9 1.1 800 2.5 43 1180 1080 90 850 75 550 80 10 0.95 650 3.0 46 1250 1150 80 790 65 580 120 11 1.2 1000 3.5 47 1220 1120 70 830 85 630 70 12 1.05 900 2.5 42 1230 1130 85 770 60 560 100

When observing the microstructure of the steel for low-temperature pressure vessel of Examples 7-12, the following facts can be found. That is, the microstructure of each embodiment of the present invention is an austenite structure from the start of the continuous casting slab solidification to a room temperature state, and after hot rolling, quenching and tempering (QT) heat treatment, the main structure of the present invention is all low-carbon It is tempered martensite, and through the quenching treatment, martensite having fine grains is obtained, and through the subsequent tempering treatment, the martensitic structure is converted into ferrite and fine precipitated carbide, while at the same time a small amount of dispersed austenite is obtained. This structure can significantly improve the toughness of the base material and is particularly suitable for manufacturing low-temperature and pressure-resistant parts. Here, the microstructure of each example has Ti(C,N) particles and MgO and/or MgS particles, and the diameters of the Ti(C,N) particles and MgO and/or MgS particles are about 0.1-8 μm, and the The quantity of Ti(C,N) particles and MgO and/or MgS particles in the cross section of the low-temperature pressure vessel steel is 5-20 pieces/mm ² .

In addition, by collecting samples of the low-temperature pressure vessel steel of Examples 7-12 and the conventional steel of Comparative Examples 1-3, various performance tests were performed on the samples, and the test results are shown in Table 8.

number Yield strengthR _el (MPa) Tensile strengthR _m (MPa) Elongation (%) Impact toughness (J) at -196°C Example 7 635 863 27 167 Example 8 630 858 26 157 Example 9 625 857 25 163 Example 10 640 862 28 150 Example 11 638 868 29 169 Example 12 642 858 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 8, the yield strength, tensile strength, elongation, and impact toughness at -196°C of each Example of the present invention were all significantly higher than the yield strength, tensile strength, elongation and impact toughness at -196°C of each comparative example. high, which explains the high mechanical properties and low temperature impact toughness of each embodiment of the present invention. In addition, each example has a tensile strength≥850 MPa, a yield strength≥625 MPa, an elongation rate≥25%, and an impact toughness≥150J at -196°C.

Examples 13-18

The steel for low-temperature pressure vessel of Examples 13-18 was manufactured through the following steps. In other words:

(1) Smelting: After converter smelting, LF+RH refining to control the mass percentage of each chemical element as shown in Table 3;

(2)Continuous Casting: Control the extraction speed to 0.9~1.2m/min, use the electromagnetic stirrer of the crystallizer during continuous casting, and the current is so that the equiaxed crystal ratio of the slab after continuous casting is ≥40% 500A, frequency controlled from 2.5 to 3.5Hz;

(3) hot rolling: including rough rolling and finish rolling, the rough rolling temperature is 1150 to 1250 ° C, the finish rolling temperature is 1050 to 1150 ° C, and the total rolling reduction is controlled to be 60 to 90%;

(4) quenching heat treatment: the temperature is 750~850℃, the holding time is 60-90min, and water cooling is carried out at the time of tapping;

(5) Tempering treatment: The temperature is 550~650℃, the holding time is 40-120min, and air cooling is performed after tapping.

The steel for low-temperature pressure vessel of Examples 13-18 further includes a polishing step before the hot rolling step.

Table 9 shows the mass percentage of each chemical element of the steel for low-temperature pressure vessel of Examples 13-18.

(wt%, the remainder is Fe and other unavoidable impurity elements other than O, P, and S) number C Si Mn Ni P S N Al Nb O Mg Example 13 0.04 0.10 0.5 11.0 0.008 0.004 0.002 0.015 0.10 0.0009 0.002 Example 14 0.08 0.30 0.3 9.0 0.003 0.003 0.003 0.03 0.13 0.0007 0.001 Example 15 0.06 0.22 0.7 10.0 0.007 0.004 0.004 0.035 0.28 0.0009 0.003 Example 16 0.02 0.35 0.8 7.0 0.009 0.005 0.005 0.05 0.2 0.0008 0.003 Example 17 0.05 0.28 0.4 12.0 0.006 0.002 0.004 0.04 0.3 0.0010 0.002 Example 18 0.03 0.18 0.6 8.0 0.004 0.005 0.003 0.025 0.18 0.0007 0.001

Table 10 shows specific process parameters of the manufacturing method of each Example.

Example number Step (2) Step (3) Step (4) Step (5) Withdrawal speed (m/min) Current (A) Frequency (Hz) Slab isometric ratio (%) Rough rolling temperature (℃) Finishing rolling temperature (℃) Total rolling reduction (%) Quenching heat treatment (℃) Holding time (min) Tempering treatment (°C) Holding time (min) 13 0.9 500 3.5 40 1150 1050 65 750 90 650 40 14 1.0 600 3.0 45 1200 1100 60 800 80 600 50 15 1.1 800 2.5 43 1180 1080 90 850 75 550 80 16 0.95 650 3.0 46 1250 1150 80 790 65 580 120 17 1.2 1000 3.5 47 1220 1120 70 830 85 630 70 18 1.05 900 2.5 42 1230 1130 85 770 60 560 100

When observing the microstructure of the steel for low-temperature pressure vessel of Examples 13-18, the following facts can be found. That is, the microstructure of each embodiment of the present invention is an austenite structure from the start of the continuous casting slab solidification to a room temperature state, and after hot rolling, quenching and tempering (QT) heat treatment, the main structure of the present invention is all low-carbon It is tempered martensite, and through the quenching treatment, martensite having fine grains is obtained, and through the subsequent tempering treatment, the martensitic structure is converted into ferrite and fine precipitated carbide, while at the same time a small amount of dispersed austenite is obtained. This structure can significantly improve the toughness of the base material and is particularly suitable for manufacturing low-temperature and pressure-resistant parts. Here, the microstructure of each example has MgO and/or MgS particles, the diameter of the MgO and/or MgS particles is about 0.1-8 μm, and the quantity of MgO and/or MgS particles in the cross section of the low-temperature pressure vessel steel is 15~55 pieces/mm ²

In addition, by collecting samples of the low-temperature pressure vessel steel of Examples 13-18 and the comparative steel of Comparative Examples 1-3, various performance tests were performed on the samples, and the test results are shown in Table 11.

number Yield strengthR _el (MPa) Tensile strengthR _m (MPa) Elongation (%) Impact toughness (J) at -196°C Example 13 637 865 26 166 Example 14 632 856 27 159 Example 15 625 858 28 160 Example 16 643 864 25 155 Example 7 636 865 27 166 Example 18 640 859 29 157 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 11, the yield strength, tensile strength, elongation and impact toughness at -196°C of each Example of the present invention are all significantly higher than the yield strength, tensile strength, elongation and impact toughness at -196°C of each comparative example. high, which explains the high mechanical properties and low temperature impact toughness of each embodiment of the present invention. In addition, each Example has tensile strength≥850 MPa, yield strength≥625 MPa, elongation≥25%, and impact toughness≥150J at -196°C.

The prior art part in the protection scope of the present invention is not limited to the embodiments provided in the present application documents, and all prior art (prior patent documents, previously published publications, previously published (including, but not limited to, the technology used as

In addition, the combination method of the technical features of the present invention is not limited by the combination method described in the claims of the present invention or the combination method described in specific embodiments, and all technical features described in the present invention are in any way as long as they do not contradict each other. can be freely combined or combined.

The above description is only a specific embodiment of the present invention, and the present invention is not limited to the above embodiment, and various similar modifications may exist. All modifications directly derived or devised by those skilled in the art based on the disclosure of the present invention shall fall within the protection scope of the present invention.

Claims (17)

A steel for low-temperature pressure vessels, comprising:
The mass percentage of a chemical element is
C: 0.02-0.08%;
Si: 0.10-0.35%;
Mn: 0.3-0.8%;
Ni: 8.0-12.0%;
N: ≤0.005%;
Al: 0.015-0.05%;
Nb: 0.1-0.3%;
Mg or Ca: 0.001-0.005%, or Mg+Ca: 0.001-0.005%;
V: ≤0.3%;
Ti: ≤0.3%; and,
Rare earth element: ≤1%; ego,
the rest is Fe and other inevitable impurities,
wherein the steel has a tensile strength of 850 MPa or more, a yield strength of 625 MPa or more, an elongation of 25% or more, and an impact toughness of 150 J or more at -196°C. According to claim 1,
The mass percentage of chemical elements is C 0.02-0.08%, Si 0.10-0.35%, Mn 0.3-0.8%, Ni 8.0-12.0%, N≤0.005%, Al 0.015-0.05%, Nb 0.1-0.3%, V 0.1- 0.3%, Ca 0.001-0.005% and rare earth elements ≤ 1%, the remainder being Fe and other unavoidable impurities; or,
The mass percentage of chemical elements is C 0.02-0.08%, Si 0.10-0.35%, Mn 0.3-0.8%, Ni 8.0-12.0%, N≤0.005%, Al 0.015-0.05%, Nb 0.1-0.3%, Ti 0.1- 0.3%, Mg 0.001-0.005% and rare earth elements ≤ 1%, the balance being Fe and other inevitable impurities; or,
The mass percentage of chemical elements is C 0.02-0.08%, Si 0.10-0.35%, Mn 0.3-0.8%, Ni 8.0-12.0%, N≤0.005%, Al 0.015-0.05%, Nb 0.1-0.3%, Mg 0.001- Steel for low-temperature pressure vessels, characterized in that 0.005% and rare earth elements ≤1%, with the remainder being Fe and other unavoidable impurities. According to claim 1,
The rare earth element is at least one selected from Ce, Hf, La, Re, Sc and Y. According to claim 1,
The microstructure is characterized in that it has (1) MgO and/or MgS particles, and/or (2) CaO and/or CaS particles, and optionally selected V(C,N) particles and/or Ti (C,N) particles. Steel for low-temperature pressure vessels. 5. The method of claim 4,
The diameters of each of the V(C,N) particles, CaO particles and CaS particles are 0.2-5 μm; The steel for low temperature pressure vessel, characterized in that the diameter of each Ti (C, N) particle, MgO particle and MgS particle is 0.1-8 μm. 5. The method of claim 4,
The low-temperature pressure vessel steel contains V and Ca, and the number of V(C,N) particles and CaO and/or CaS particles in the cross section of the low-temperature pressure vessel steel is 5-20 pieces/mm ² ; or,
The low-temperature pressure vessel steel contains Ti and Mg, and the quantity of Ti (C,N) particles and MgO and/or MgS particles is 5 to 25 pieces/mm ² ; or,
The steel for low-temperature pressure vessel contains Mg, does not contain Ca, Ti and V, and the quantity of MgO and/or MgS particles is 15 to 55 pieces/mm ² Steel for low-temperature pressure vessel. 3. The method of claim 2,
The mass percentage of V is 0.1-0.2%; Steel for low-temperature pressure vessels, characterized in that the mass percentage of Ti is 0.1-0.2%. 3. The method of claim 2,
The mass percentage of Ca is 0.001-0.003%; Steel for low-temperature pressure vessels, characterized in that the mass percentage of Mg is 0.001-0.003%. delete The method for manufacturing the steel for a low-temperature pressure vessel according to any one of claims 1 to 8, comprising:
(1)Smelting: After converter smelting, LF+RH refining;
(2) continuous casting;
(3) hot rolling, the hot rolling step (3) includes rough rolling and finish rolling, the rough rolling temperature is controlled to 1150 to 1250 ℃, the finish rolling temperature is controlled to 1050 to 1150 ℃, total Controlled rolling reduction to 60-95%;
(4) quenching heat treatment, where the quenching heat treatment temperature is 750~850℃, the holding time is 60-90min, and water cooling proceeds when the steel is discharged from a furnace;
(5) tempering treatment; Here, the tempering treatment temperature is 550 ~ 650 ℃, the holding time is 40-120 min, and air cooling proceeds after being discharged from a furnace;
A manufacturing method comprising the steps of. 11. The method of claim 10,
A manufacturing method, characterized in that it further comprises a polishing step before the hot rolling step. 11. The method of claim 10,
Manufacturing method, characterized in that by controlling the withdrawal speed in the step (2) to 0.9 ~ 1.2 m / min. 11. The method of claim 10,
In the above step (2), the electromagnetic stirrer of the crystallizer is used during continuous casting, and the current is 500-1000A and the frequency is controlled to 2.5 to 3.5 Hz so that the equiaxed crystal ratio of the slab after continuous casting is ≥ 40% A manufacturing method, characterized in that. delete delete delete delete