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WO2019037749A1 - 一种低温压力容器用钢及其制造方法 - Google Patents

一种低温压力容器用钢及其制造方法 Download PDF

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Publication number
WO2019037749A1
WO2019037749A1 PCT/CN2018/101858 CN2018101858W WO2019037749A1 WO 2019037749 A1 WO2019037749 A1 WO 2019037749A1 CN 2018101858 W CN2018101858 W CN 2018101858W WO 2019037749 A1 WO2019037749 A1 WO 2019037749A1
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WO
WIPO (PCT)
Prior art keywords
steel
pressure vessel
low
temperature pressure
particles
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/CN2018/101858
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English (en)
French (fr)
Inventor
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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Publication date
Priority claimed from CN201710731755.2A external-priority patent/CN109423570B/zh
Priority claimed from CN201710731249.3A external-priority patent/CN109423569B/zh
Application filed by Baoshan Iron and Steel Co Ltd filed Critical Baoshan Iron and Steel Co Ltd
Priority to KR1020207006798A priority Critical patent/KR102364473B1/ko
Priority to JP2020511260A priority patent/JP7024063B2/ja
Publication of WO2019037749A1 publication Critical patent/WO2019037749A1/zh
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/46—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/16—Control of thickness, width, diameter or other transverse dimensions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10—Supplying or treating molten metal
    • B22D11/11—Treating the molten metal
    • B22D11/114—Treating the molten metal by using agitating or vibrating means
    • B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/16—Controlling or regulating processes or operations
    • B22D11/20—Controlling or regulating processes or operations for removing cast stock
    • 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
    • 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
    • C21D1/62—Quenching devices
    • C21D1/63—Quenching devices for bath quenching
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • the present invention relates to a steel and a method of manufacturing the same, and more particularly to a nickel-containing steel and a method of manufacturing the same for use in a cryogenic pressure vessel.
  • 9% Ni steel refers to low carbon steel with a Ni content of about 9%. It was founded in the product research laboratory of the International Nickel Company of the United States, and the minimum operating temperature is -196 °C. In 1952, the first 9% Ni steel storage tank was put into use in the United States. Japan built the first LNG cryogenic storage tank in China in 1969. The maximum tank capacity of the tanks built has reached 20 ⁇ 10 4 m 3 . As the newly added proven reserves of domestic natural gas continue to grow, the government is increasingly paying attention to the development and utilization of natural gas and the design and construction of its cryogenic storage equipment. In the 1980s, in the Daqing Ethylene Project, a large 9% Ni steel vinyl spherical tank was successfully built for the first time.
  • the low temperature mechanical properties of 9% Ni steel are mainly determined by the chemical composition, especially the content of Ni and C elements.
  • the toughness of the steel depends on the purity of the steel as well as the microstructure.
  • Ni steel adopts the continuous casting steelmaking process.
  • the metallurgical treatment in the steel casting process, the vacuum degassing process and the high purity of the steel play an extremely important role in improving the low temperature toughness of the steel. Since the presence of impurity elements such as P, S deteriorates the low temperature toughness of the steel, it is necessary to strictly control the content of impurity elements such as P, S to a relatively low level.
  • Table 1 Chemical composition (wt%) of related typical steel grades in the prior art
  • One of the objects of the present invention is to provide a steel for a low temperature pressure vessel which adopts a microalloy addition design without adding excessive expensive elements such as Ni by adding an appropriate amount of Nb, and Ca and/or Mg elements and optionally V and / or Ti, control the lower content of total oxygen, so that the steel for low temperature pressure vessel has higher strength, good molding performance and low temperature impact toughness, and the cost of steel material is lower than that of the prior art.
  • the present invention provides a steel for a low-temperature pressure vessel having a chemical element mass distribution ratio of 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%; balance is Fe and other unavoidable impurities And the sum of the mass distribution ratios of Ca and Mg is 0.001-0.005%.
  • the steel for a cryogenic pressure vessel of the present invention contains only at least one or two of Ca and Mg, and does not contain V and Ti.
  • the chemical element mass distribution ratio 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%, Ni7.0-12.0%, N ⁇ 0.005 %, Al 0.015-0.05%, Nb 0.1-0.3%, Ca and/or Mg 0.001-0.005%; the balance is Fe and other unavoidable impurities.
  • 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 distribution ratios of V and Ti is in the range of 0.1 to 0.3%. Therefore, in these embodiments, the chemical element mass distribution ratio 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 balance is Fe and other unavoidable impurities.
  • the steel for low temperature pressure vessel of the present invention contains V and Ca, and the chemical element mass ratio 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 0.1-0.3%, Ca 0.001-0.005%; the balance is Fe and other unavoidable impurities.
  • the low temperature pressure vessel has a chemical element mass distribution ratio of 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 balance is Fe and other unavoidable impurities.
  • the steel for low temperature pressure vessel of the present invention contains Ti and Mg having a chemical element mass ratio of 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%, Ti 0.1-0.3%, Mg 0.001-0.005%; the balance is Fe and other unavoidable impurities.
  • the steel for low temperature pressure vessel of the present invention contains only Mg, does not contain Ca, Ti and V, and has a chemical element mass distribution ratio of 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%); balance is Fe and other unavoidable impurities .
  • the steel for low temperature pressure vessel of the present invention forms Nb (C, N) by adding an appropriate amount of Nb, which is advantageous for improving strength and improving impact toughness; moreover, by adding Ca and/or Mg and optionally V and/or Ti can significantly improve the low temperature impact toughness of the steel while taking into account the effect of increasing the strength of the steel.
  • the microstructure of the steel for the low-temperature pressure vessel is evolved as follows: from the solidification of the continuous casting slab to the austenite structure at room temperature.
  • the main structures treated by quenching + tempering (QT) heat treatment are low carbon tempered martensite.
  • the quenching treatment can obtain martensite with fine grain, and the subsequent tempering treatment converts the martensite structure into ferrite and fine precipitated carbide, and a small amount of diffused austenite can be obtained.
  • the toughness of the base metal is greatly improved, and it is especially suitable for the manufacture of parts that are resistant to low temperature and pressure.
  • the mass percentage of C mainly affects the precipitation amount and precipitation temperature range of the carbide.
  • carbon has a certain strengthening effect, and controlling the lower mass percentage of C is advantageous for improving the impact toughness of the steel.
  • an excessively high mass percentage of carbon reduces the corrosion resistance of the material.
  • the mass percentage of C is controlled to 0.02-0.08%. In certain embodiments, the mass percentage of C is controlled to be 0.02-0.06%.
  • Si can be increased in strength in steel, but Si is also detrimental to the formability and toughness of steel.
  • the mass percentage of Si to be controlled in the steel for a low temperature pressure vessel according to the present invention is from 0.10 to 0.35%, preferably from 0.10 to 0.30%.
  • Mn is an austenite element, which suppresses the harmful effects of S in a nickel-based corrosion-resistant alloy and improves thermoplasticity.
  • too high a mass percentage of Mn is detrimental to its corrosion resistance. Therefore, considering the mechanical properties and corrosion resistance, the low temperature pressure vessel of the present invention is limited to a mass percentage of Mn of 0.3 to 0.8%, preferably 0.35 to 0.7%.
  • Ni is a main element in the steel for a low-temperature pressure vessel according to the present invention, and has excellent austenite phase stability, and can improve the mechanical properties and impact toughness of the steel for a low-temperature pressure vessel according to the present invention.
  • the tensile strength at high temperature gradually increases. This is because when the mass percentage of Ni is low, most of Ni is dissolved in austenite, expanding the austenite phase region and increasing the recrystallization temperature. The mechanical properties of the alloy are improved and 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%, preferably 7.5 to 10.5%.
  • N is a stable austenite element.
  • the N having a lower percentage of controlled mass is advantageous for improving the impact toughness of the steel for the low temperature pressure vessel.
  • higher mass percentages of nitrogen tend to result in reduced toughness and ductility of the steel and also reduce 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 ⁇ 0.005%.
  • the alloy is strengthened mainly by controlling the oxygen content in the steel by Al, thereby affecting the dislocation behavior.
  • Increasing the mass percentage of Al can significantly increase the solution temperature and creep strength, but the excessive mass percentage of Al impairs the plasticity of the steel.
  • the addition of Al is beneficial to improve the elongation and deformation properties of the steel, thereby improving the processing properties of the steel.
  • an Al content of more than 0.05% by mass is required to lower the impact toughness of the steel. Based on the above considerations, 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%, preferably 0.02 to 0.04%.
  • 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.
  • Nb is a strong carbonitride forming element, and combines with carbon and nitrogen to form Nb (C, N), which is beneficial to improve strength and improve impact. toughness.
  • C, N carbonitride forming element
  • carbon and nitrogen have a certain strengthening effect.
  • Some Nb in the steel forms Nb (C, N), which can strengthen the austenite phase matrix, refine the austenite grains, and strengthen the austenite grain boundaries. It is advantageous to improve the low temperature impact toughness of the steel for low temperature pressure vessels. Therefore, the mass percentage of Nb in the steel for a low temperature pressure vessel according to the present invention is limited to 0.1 to 0.3%, preferably 0.1 to 0.2%.
  • Mg Micro-magnesium segregation at grain boundaries reduces grain boundary energy and phase boundary energy, improves and refines the morphology of grain boundary carbides and other grain boundary precipitation phases, such as blocking or spheroidizing carbides, effectively inhibiting grain boundary sliding Reduce the grain boundary stress concentration and eliminate the notch sensitivity.
  • magnesium and sulfur and other harmful impurities form high melting point compounds MgO and MgS, etc., purify the grain boundary, so that the concentration of impurity elements such as S, O, P, etc. at the grain boundary is significantly reduced, and the harm of impurity elements is reduced.
  • MgO and MgS in the steel can be used as nucleation sites to refine grains. Trace magnesium improves plasticity, improves high temperature tensile ductility, and increases impact toughness and fatigue strength.
  • Ca can change the composition, quantity and morphology of non-metallic inclusions in steel.
  • calcium can refine the grain of steel, deoxidize and desulfurize, and CaO and CaS can be used as nucleation sites to refine the solidified structure.
  • the steel for low temperature pressure vessel of the present invention contains any one or both of Ca and Mg, and the content of Ca is 0-0.005%, such as 0.001-0.005%; the content of Mg is 0-0.005%, such as 0.001-0.005 %; the condition is that the sum of the contents of Ca + Mg is in the range of 0.001 - 0.005%.
  • the steel for low temperature pressure vessel of the present invention contains only Mg in an amount ranging from 0.001 to 0.005%, preferably from 0.001 to 0.003%.
  • V:V refines the grain of the structure and improves strength and toughness.
  • vanadium is a strong carbide forming element and has a strong binding bond with carbon to form a stable VC. It is a typical high melting point, high hardness, high dispersion carbide, and is an element that strongly improves wear resistance.
  • the particles that form during the tempering process or form VC at other stages are finely dispersed.
  • the rhodium-vanadium compound is added in a higher strength than the Nb alone.
  • the austenite grains can be further refined, so that the ferrite grains after cooling are finer, which is advantageous for improving strength and toughness.
  • Ti has solid solution strengthening and precipitation strengthening in steel, and it has strong binding ability with O, which can reduce the oxygen content in steel.
  • Ti combines with C and N to form Ti(C, N), which can refine the solidified structure.
  • alloys containing higher Ni, especially under the combined action of Nb and Al the addition of Ti forms Ni 3 (Al, Ti, Nb), which improves the strength and toughness of the steel.
  • the steel for low temperature pressure vessel of the present invention may further contain any one or both of V and Ti, and the content of V is 0-0.3%, such as 0.1-0.3%; and the content of Ti is 0-0.3%, such as 0.1-0.3%. In certain embodiments, when V and/or Ti are included, the sum of the V+Ti contents is in the range of 0.1-0.3%.
  • the unavoidable impurity elements include O, P, and S.
  • O is mainly present as an oxide inclusion, and a high total oxygen content indicates that there are many inclusions, and reducing the total oxygen content is advantageous for improving the comprehensiveness of the material, and thus the above-mentioned unavoidable impurity elements are described above.
  • the mass percentage of the steel for the low temperature pressure vessel is controlled by: total oxygen ⁇ 0.001%, P ⁇ 0.010%, S ⁇ 0.005%.
  • the chemical element further has a rare earth element having a mass distribution ratio of ⁇ 1%, such as 0.1-1%.
  • the rare earth element includes 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 a low-temperature pressure vessel of the present invention, and the total mass percentage of the rare earth element to be added is ⁇ 1%.
  • the rare earth element acts as a purifying agent, and has the functions of deoxidation and desulfurization, thereby reducing the harmful effects of oxygen and sulfur at the grain boundary; in addition, the rare earth element is segregated at the grain boundary as a microalloying element, To strengthen the grain boundary; and, as an active element, the rare earth element improves the oxidation resistance of the alloy and improves the surface stability.
  • Nb CN particles, MgO and/or MgS particles and/or CaO and/or CaS particles in the microstructure, optionally containing V ( C, N) particles and / or Ti (C, N) particles.
  • V and Ti or a combination thereof and Mg and Ca or a combination thereof When an element selected from the group consisting of V and Ti or a combination thereof and Mg and Ca or a combination thereof is added to the steel for a low-temperature pressure vessel according to the present invention, a small amount of V (C, N) is formed in the alloy during cooling and solidification. And/or Ti(C, N) and CaO and/or MgO and/or CaS particles and/or MgS particles.
  • the above particles are advantageous for refining and stabilizing the austenite grains, thereby avoiding the formation of crack defects on the surface of the continuous casting billet or the hot rolled sheet by the steel for the low temperature pressure vessel, and also improving the low temperature impact toughness of the material.
  • the particles when V(C, N) particles are contained, the particles have a diameter of about 0.2 to 5 ⁇ m; when CaO and/or CaS particles are contained, the particles are The diameter is about 0.2-5 ⁇ m; when containing Ti(C,N) particles, the particles have a diameter of about 0.1-8 ⁇ m; when MgO and/or MgS particles are contained, the particles have a diameter of about 0.1-8 ⁇ m.
  • the number of V(C, N) particles in the cross section of the steel for the low-temperature pressure vessel is 5 to 20/mm 2 .
  • the number of CaO and/or CaS particles is 5 to 20 / mm 2
  • the number of Ti (C, N) particles is 5 to 25 / mm 2
  • the number of MgO and / or MgS particles is 5 to 25 / mm 2 .
  • the amount of MgO and/or MgS particles and/or CaO and/or CaS is 15 to 55 / mm 2 .
  • the mass percentage thereof when V is contained only, the mass percentage thereof is 0.1-0.2%; and when Ti is contained only, the mass percentage thereof is 0.1-0.2%; or When both V and Ti are contained, the sum of the mass percentages of the two is 0.1-0.2%.
  • the mass percentage thereof when Ca is contained only, the mass percentage thereof is 0.001 to 0.003%; or when only Mg is contained, the mass percentage thereof is 0.001 to 0.003%; When both Ca and Mg are contained, the sum of the mass percentages of the two is 0.001 to 0.003%.
  • the chemical element mass percent ratio of the steel for cryogenic pressure vessels of the present invention is:
  • Si 0.10-0.35%, preferably 0.1-0.3%;
  • Mn 0.3-0.8%, preferably 0.35-0.7%;
  • 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%;
  • the balance is Fe and other unavoidable impurities.
  • the chemical element mass ratio of the steel for cryogenic pressure vessels of the present invention is:
  • Mg 0.001-0.003%
  • Ca 0.001-0.003%
  • Mg+Ca 0.001-0.003%
  • the balance is Fe and other unavoidable impurities.
  • the tensile strength is ⁇ 850 MPa
  • the yield strength is ⁇ 625 MPa
  • the elongation is ⁇ 25%
  • the impact toughness at -196 ° C is ⁇ 150 J.
  • the steel for low temperature pressure vessel according to the present invention has a tensile strength of 850-870 MPa, a yield strength of 625-650 MPa, an elongation of 25-30%, and an impact toughness at -196 °C. 150-170J.
  • Another object of the present invention is to provide a method for producing a steel for a low temperature pressure vessel as described above, which comprises the steps of:
  • a small amount of ferrovanadium and/or ferrotitanium is added at the end of RH refining to add V and/or Ti, and a calcium wire is fed to add Ca and/or a nickel-magnesium alloy to be added to add Mg.
  • soft agitation of the argon blowing gas is performed, and the flow rate of the argon gas is controlled at 5 to 8 liters/min.
  • the control of the pulling speed is 0.9 to 1.2 m/min.
  • step (2) electromagnetic stirring is performed by a crystallizer during continuous casting, and the control current is 500-1000 A and the frequency is 2.5-3.5 Hz, so that after continuous casting The slab equiaxed crystal ratio is ⁇ 40%.
  • the step (3) includes rough rolling and finish rolling, wherein the rough rolling temperature is controlled to be 1150 to 1250 ° C, and the finishing rolling temperature is 1050 to 1150 ° C.
  • the total reduction ratio is controlled to be 60 to 95%, such as 60 to 90%.
  • the quenching heat treatment temperature is 750 to 850 ° C
  • the holding time is 60 to 90 min
  • water cooling is performed at the time of discharging.
  • the tempering treatment temperature is 550 to 650 ° C
  • the holding time is 40 to 120 min
  • air cooling is performed after the furnace is discharged.
  • the steel for low temperature pressure vessel according to the present invention adopts a microalloy addition design, and does not need to add excessive expensive elements such as Ni, and is controlled by adding an appropriate amount of Nb, V and/or Ti, Ca and/or Mg elements.
  • the low content of total oxygen makes the steel for low temperature pressure vessel have higher strength, good molding performance and low temperature impact toughness, and the steel material cost is lower than that of the prior art.
  • the steel for the low temperature pressure vessel of Examples 1-6 was obtained by the following steps:
  • control pull speed control is 0.9 ⁇ 1.2m/min, electromagnetic stirring is used in continuous casting, control current is 500-1000A, frequency is 2.5 ⁇ 3.5Hz, so that slab after continuous casting, etc.
  • Hot rolling including rough rolling and finish rolling, wherein the rough rolling temperature is controlled to be 1150 to 1250 ° C, the finishing rolling temperature is 1050 to 1150 ° C, and the total pressure control efficiency is 60 to 90%;
  • tempering treatment the temperature is 550 ⁇ 650 ° C, the holding time is 40-120 min, and the air is cooled.
  • the steel for a low temperature pressure vessel of Examples 1-6 further has a grinding step before the hot rolling step.
  • Comparative steels of Comparative Examples 1-3 were prepared using the prior art.
  • Table 3 lists the mass ratios of the respective chemical elements in the steel for the low temperature pressure vessel of Examples 1-6 and the comparative steel of Comparative Examples 1-3.
  • Table 4 lists the specific process parameters of the manufacturing method of each example.
  • the microstructure of the steel for low temperature pressure vessel of the above Examples 1-6 was austenite structure from the solidification of the continuous casting slab to the room temperature, and was subjected to hot rolling.
  • the main structure of the case is low carbon tempered martensite, in which quenching treatment can obtain fine grained martensite, followed by tempering treatment to make martensite
  • the structure is transformed into ferrite and fine precipitated carbides, and a small amount of dispersed austenite is obtained.
  • This structure can greatly improve the toughness of the base metal, and is particularly suitable for manufacturing parts that are resistant to low temperature and pressure.
  • each embodiment has V(C, N) particles and CaO and/or CaS particles, the V(C, N) particles, CaO and/or CaS particles having a diameter of about 0.2-5 ⁇ m,
  • the number of V (C, N) particles and CaO and/or CaS particles in the cross section of the steel for the low temperature pressure vessel is 5 to 20 / mm 2 .
  • the yield strength, tensile strength, elongation and impact toughness at -196 °C of the examples in this case were significantly higher than the yield strength, tensile strength, elongation and -196 ° C of each comparative example.
  • Impact toughness indicating that the mechanical properties and low temperature impact toughness of the examples in the present case are high.
  • the tensile strength was ⁇ 850 MPa
  • the yield strength was ⁇ 625 MPa
  • the elongation was ⁇ 25%
  • the impact toughness at -196 ° C was ⁇ 150 J.
  • the steel for the low temperature pressure vessel of Examples 7-12 was obtained by the following steps:
  • control pull speed control is 0.9 ⁇ 1.2m/min, electromagnetic stirring is used in continuous casting, control current is 500A, frequency is 2.5 ⁇ 3.5Hz, so that the slab equiaxed crystal after continuous casting The ratio is ⁇ 40%;
  • Hot rolling including rough rolling and finish rolling, wherein the rough rolling temperature is controlled to be 1150 to 1250 ° C, the finishing rolling temperature is 1050 to 1150 ° C, and the total pressure control efficiency is 60 to 90%;
  • tempering treatment the temperature is 550 ⁇ 650 ° C, the holding time is 40-120 min, and the air is cooled.
  • the steel for a low temperature pressure vessel of Examples 7 to 12 also has a grinding step before the hot rolling step.
  • Table 6 lists the mass ratios of the chemical elements of the steel for the low temperature pressure vessel of Examples 7-12.
  • 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 0.99 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 lists the specific process parameters of the manufacturing method of each example.
  • the microstructure of the steel for low temperature pressure vessel of the above Examples 7-12 was observed, and it can be found that the microstructure of each embodiment of the present invention is austenite structure from the solidification of the continuous casting slab to the room temperature, and the heat is passed through the heat.
  • the main structure of the case is low carbon tempered martensite, in which quenching treatment can obtain fine grained martensite, and then tempering treatment makes Markov
  • the bulk structure is transformed into ferrite and fine precipitated carbides, and a small amount of dispersed austenite is obtained.
  • This structure can greatly improve the toughness of the base metal, and is particularly suitable for manufacturing parts that are resistant to low temperature and pressure.
  • the microstructure of each embodiment 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 about 0.1-8 ⁇ m,
  • the number of Ti (C, N) particles and MgO and/or MgS particles in the cross section of the steel for the low temperature pressure vessel is 5 to 25 / mm 2 .
  • the yield strength, tensile strength, elongation and impact toughness at -196 °C of the examples in this case were significantly higher than the yield strength, tensile strength, elongation and -196 ° C of each comparative example.
  • Impact toughness indicating that the mechanical properties and low temperature impact toughness of the examples in the present case are high.
  • the tensile strength was ⁇ 850 MPa
  • the yield strength was ⁇ 625 MPa
  • the elongation was ⁇ 25%
  • the impact toughness at -196 ° C was ⁇ 150 J.
  • the steel for the low temperature pressure vessel of Examples 13-18 was obtained by the following steps:
  • control pull speed control is 0.9 ⁇ 1.2m/min, electromagnetic stirring is used in continuous casting, control current is 500A, frequency is 2.5 ⁇ 3.5Hz, so that the slab equiaxed crystal after continuous casting The ratio is ⁇ 40%;
  • Hot rolling including rough rolling and finish rolling, wherein the rough rolling temperature is controlled to be 1150 to 1250 ° C, the finishing rolling temperature is 1050 to 1150 ° C, and the total pressure control efficiency is 60 to 90%;
  • tempering treatment the temperature is 550 ⁇ 650 ° C, the holding time is 40-120 min, and the air is cooled.
  • the steel for the low temperature pressure vessel of Examples 13 to 18 also has a grinding step before the hot rolling step.
  • Table 9 lists the mass ratios of the chemical elements of the steel for the low temperature pressure vessel of Examples 13-18.
  • 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 0.99 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 lists the specific process parameters of the manufacturing method of each example.
  • the microstructure of the steel for low temperature pressure vessel of the above-mentioned Examples 13-18 in the present invention was observed, and it was found that the microstructure of each embodiment of the present invention was austenite structure from the solidification of the continuous casting slab to the room temperature, and the heat was passed through.
  • the main structure of the case is low carbon tempered martensite, in which quenching treatment can obtain fine grained martensite, and then tempering treatment makes Markov
  • the bulk structure is transformed into ferrite and fine precipitated carbides, and a small amount of dispersed austenite is obtained. This structure can greatly improve the toughness of the base metal, and is particularly suitable for manufacturing parts that are resistant to low temperature and pressure.
  • the microstructure of each embodiment has MgO and/or MgS particles having a diameter of about 0.1-8 ⁇ m, in the cross section of the steel for the low temperature pressure vessel, MgO and/or MgS particles The number is 15 to 55 / mm 2 .
  • the yield strength, tensile strength, elongation and impact toughness at -196 °C of the examples in this case were significantly higher than the yield strength, tensile strength, elongation and -196 ° C of each comparative example.
  • Impact toughness indicating that the mechanical properties and low temperature impact toughness of the examples in the present case are high.
  • the tensile strength was ⁇ 850 MPa
  • the yield strength was ⁇ 625 MPa
  • the elongation was ⁇ 25%
  • the impact toughness at -196 ° C was ⁇ 150 J.

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Abstract

一种低温压力容器用钢，其化学元素质量百分配比为：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和/或Mg 0.001-0.005％、任选的V和/或Ti 0.1-0.3％；余量为Fe和其他不可避免的杂质。上述低温压力容器用钢的制造方法，包括步骤：(1)冶炼：转炉冶炼，然后LF+RH精炼；(2)连铸；(3)热轧；(4)淬火热处理；(5)回火处理。所述的低温压力容器用钢低温冲击韧性高。

Description

一种低温压力容器用钢及其制造方法 技术领域
本发明涉及一种钢及其制造方法，尤其涉及一种含镍的钢及其制造方法，该钢用于低温压力容器。
背景技术
9％Ni钢是指Ni元素含量约为9％的低碳钢，始创于美国国际镍公司的产品研究试验室，最低使用温度可达-196℃。1952年，第一台9％Ni钢储罐在美国投入使用。日本于1969年建造了国内第一台液化天然气低温储罐，所建储罐的最大罐容目前已达20×l0 4m 3。随着国内天然气新增探明储量的不断增长，政府也日益重视天然气的开发利用及其低温储存设备的设计和建造。20世纪8O年代在大庆乙烯工程中，首次成功建造了大型9％Ni钢乙烯球罐。2004年，国内首个大型低温液化天然气项目——广东液化天然气工程开工，单台储罐容积达到16×10 4m 3。迄今为止，9％Ni钢在液化天然气设备中的应用已有60多年的历史。因其具有优良的低温韧性及良好的焊接性能，9％Ni钢已成为国际上低温设备领域广泛使用的钢种。
9％Ni钢的低温力学性能主要决定于化学成分，尤其是Ni、C元素的含量。此外，该钢的韧性还取决于钢的纯净度以及微观组织。
9％Ni钢的生产采用了连铸炼钢工艺，铸钢过程中的冶金处理、真空除气工艺以及钢的高纯净度对改善钢的低温韧性都起着极其重要的作用。由于P，S等杂质元素的存在会恶化钢的低温韧性，因此需要将P，S等杂质元素的含量严格控制在较低水平。
日本于1977年将9％Ni钢纳入JIS标准。同年，美国也将9％Ni钢列入了ASME和ASTM标准中。各主要工业国家9％Ni钢的代号、化学成分和力学性能见表1和表2。
表1：现有技术中的相关典型钢种的化学成分(wt％)
Figure PCTCN2018101858-appb-000001
表2：现有技术中相关典型钢种的力学性能
Figure PCTCN2018101858-appb-000002
由表1和表2可见，现有技术中的低温压力容器用钢越来越无法满足日益提高的使用和制造要求。鉴于此，期望获得一种低温压力容器用钢，该低温压力容器的力学性能、低温冲击韧性相较于现有技术而言得到提高，且生产该低温压力容器用钢的生产成本更为经济节约。
发明内容
本发明的目的之一在于提供一种低温压力容器用钢，采用微合金添加设计，不需要添加过多的昂贵元素例如Ni，通过添加适量的Nb、和Ca和/或Mg元素 以及任选的V和/或Ti，控制较低含量的总氧，使得低温压力容器用钢具有较高的的强度、良好的成型性能以及低温冲击韧性，且钢材料成本相较于现有技术而言较低。
基于上述发明目的，本发明提供一种低温压力容器用钢，其化学元素质量百分配比为：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％和Ti 0-0.3％；余量为Fe和其他不可避免的杂质；且Ca与Mg的质量百分配比之和为0.001-0.005％。
在某些实施方案中，本发明的低温压力容器用钢仅含有Ca和Mg中的至少一种或两种，而不含有V和Ti。在这些实施方案中，本发明低温压力容器用钢的化学元素质量百分配比为：C 0.02-0.08％、Si 0.10-0.35％、Mn 0.3-0.8％、Ni7.0-12.0％、N≤0.005％、Al 0.015-0.05％、Nb 0.1-0.3％、Ca和/或Mg 0.001-0.005％；余量为Fe和其他不可避免的杂质。
在某些实施方案中，本发明的低温压力容器用钢还含有V和Ti中的至少一种或两种，V与Ti的质量百分配比之和在0.1-0.3％的范围内。因此，在这些实施方案中，本发明低温压力容器用钢的化学元素质量百分配比为：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％、Nb0.1-0.3％、V和/或Ti 0.1-0.3％、Ca和/或Mg 0.001-0.005％；余量为Fe和其他不可避免的杂质。
在某些实施方案中，本发明的低温压力容器用钢含有V和Ca，其化学元素质量百分配比为：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 0.1-0.3％、Ca 0.001-0.005％；余量为Fe和其他不可避免的杂质。在某些实施方案中，所述低温压力容器用钢化学元素质量百分配比为：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％；余量为Fe和其他不可避免的杂质。
在某些实施方案中，本发明的低温压力容器用钢含有Ti和Mg，其化学元素质量百分配比为：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％、Ti 0.1-0.3％、Mg 0.001-0.005％；余量 为Fe和其他不可避免的杂质。
在某些实施方案中，本发明的低温压力容器用钢仅含有Mg，不含有Ca、Ti和V，其化学元素质量百分配比为：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％(优选0.001-0.003％)；余量为Fe和其他不可避免的杂质。
相较于现有技术中，本发明所述的低温压力容器用钢通过添加适量的Nb，从而形成Nb(C、N)，有利于提高强度、改善冲击韧性；此外，通过添Ca和/或Mg以及任选的加V和/或Ti可显著改善钢的低温冲击韧性，同时兼顾了提高钢强度的作用。
此外，在本案中，所述低温压力容器用钢的微观组织演化如下：从连铸板坯凝固开始到室温状态下均为奥氏体组织。再经过热轧后，采用淬火+回火(QT)热处理的主要组织均为低碳回火马氏体。其中，淬火处理可获得晶粒细小的马氏体，其后的回火处理使马氏体结构又转变为铁素体和细小的析出碳化物，同时可获得少量的弥散奥氏体，可使母材的韧性大大改善，特别适用于制造耐低温可承压的零部件。
本发明所述的低温压力容器用钢的各化学元素的设计原理为：
C：通常C的质量百分比主要影响碳化物的析出量和析出温度范围。在本发明所述的低温压力容器用钢中，碳具有一定的强化作用，控制较低的C的质量百分比有利于改善该钢的冲击韧性。但是，过高的碳的质量百分比会降低材料的耐蚀性能。为了兼顾力学性能和冲击韧性，将C的质量百分比控制在0.02-0.08％。在某些实施方案中，将C的质量百分比控制为0.02-0.06％。
Si：Si在钢中可以提高的强度，但是，Si也会对钢的成型性和韧性不利。在本发明所述的低温压力容器用钢中控制Si的质量百分比在0.10-0.35％，优选0.10-0.30％。
Mn：Mn为奥氏体元素，可抑制镍基耐蚀合金中S的有害作用，改善热塑性。但是，Mn的质量百分比过高不利于保证其耐腐蚀性。因此，综合考虑力学性能和耐腐蚀性，本发明所述的低温压力容器对Mn的质量百分比限定在0.3-0.8％，优选0.35～0.7％。
Ni：Ni是本发明所述的低温压力容器用钢中的主要元素，具有很好的奥氏 体相稳定性，可以改善本发明所述的低温压力容器用钢的力学性能和冲击韧性。随着Ni增加，高温拉伸强度逐渐升高，这是因为当Ni的质量百分比较低时，Ni大部分固溶于奥氏体中，扩大奥氏体相区，提高了再结晶温度，使合金力学性能得以提高改善。因此，在本发明所述的低温压力容器用钢中对Ni的质量百分比限定在7.0-12.0％，优选7.5～10.5％。
N：N是稳定奥氏体元素。控制质量百分比较低的N有利于改善所述的低温压力容器用钢的冲击韧性。然而，质量百分比较高的氮易导致钢的韧性和延展性减少，并且也会降低钢的可热加工性。因此，在本发明所述的低温压力容器用钢中对N的质量百分比限定在N≤0.005％。
Al：在本发明所述的技术方案中，主要通过Al控制钢中氧含量，从而影响位错行为来强化合金。增加Al的质量百分比可以明显地提高固溶温度、蠕变强度，但过高的Al的质量百分比有损钢的塑性。此外，添加Al有利于改善钢的延伸变形性能，从而改善钢的加工性能。但需要质量百分比高于0.05％的Al含量会降低钢的冲击韧性。基于上述考虑，在本发明所述的低温压力容器用钢中对Al的质量百分比限定在0.015-0.05％，优选0.02～0.04％。
Nb：Nb是常用固溶强化元素之一。Nb的原子半径较Ni、Co、Fe原子大15～18％，此外，Nb是很强的碳氮化物形成元素，与碳、氮结合成Nb(C、N)，有利于提高强度、改善冲击韧性。同时，碳和氮具有一定的强化作用，钢中部分Nb形成Nb(C、N)，可以强化奥氏体相基体、细化奥氏体晶粒，也可以强化奥氏体晶界，从而有利于改善所述的低温压力容器用钢的低温冲击韧性。因此，在本发明所述的低温压力容器用钢中对Nb的质量百分比限定在0.1-0.3％，优选0.1～0.2％。
Mg：微量镁在晶界偏聚降低晶界能和相界能，改善和细化晶界碳化物及其他晶界析出相的形态，例如使碳化物块化或球化，有效抑制晶界滑动，降低晶界应力集中，消除缺口敏感性。此外，镁与硫等有害杂质形成高熔点的化合物MgO和MgS等，净化晶界，使晶界的S、O、P等杂质元素浓度明显降低，减少杂质元素的危害。凝固过程中，钢中MgO和MgS等可作为形核质点细化晶粒。微量镁提高塑性，改善高温拉伸塑性，增加冲击韧性和疲劳强度。
Ca：钙可以改变钢中非金属夹杂物的成分、数量及形态；此外，加钙还能细 化钢的晶粒，脱氧去硫，形成的CaO和CaS可作为形核质点细化凝固组织。改善钢的耐蚀性、耐磨性、耐高温、耐低温性能；提高钢的塑性、冲击韧性、疲劳强度和焊接性能；增强钢的抗热裂、抗氢致裂纹和抗层状撕裂能力。
本发明的低温压力容器用钢含有Ca和Mg中的任意一种或全部两种，Ca的含量为0-0.005％，如0.001-0.005％；Mg的含量为0-0.005％，如0.001-0.005％；条件是，Ca+Mg的含量之和在0.001-0.005％的范围内。在某些实施方案中，本发明的低温压力容器用钢仅含有Mg，其含量在0.001-0.005％的范围内，优选在0.001-0.003％的范围内。
V：V可细化组织晶粒，提高强度和韧性。为了使淬火后获得细晶马氏体，加入钒是比较有效的手段。钒是强碳化物形成元素，与碳的结合力极强，形成稳定的VC，是典型的高熔点、高硬度、高弥散度碳化物，是强烈提高耐磨性的元素。无论在回火过程中析出，还是在其他阶段形成VC的质点都是细小弥散的。铌-钒复合加入，其强度比单独加入Nb的高。同时可使奥氏体晶粒进一步细化，使冷却后的铁素体晶粒更细小，有利于提高强度和韧性。
Ti：Ti在钢中具有固溶强化和沉淀强化作用，其与O结合能力强，可降低钢中氧含量。此外，Ti与C、N结合形成Ti(C、N)，可细化凝固组织。在含Ni较高的合金中，特别是在Nb和Al的共同作用下，添加Ti可形成Ni 3(Al,Ti,Nb)，提高钢的强度和韧性。
本发明的低温压力容器用钢中还可含有V和Ti中的任意一种或全部两种，V的含量为0-0.3％，如0.1-0.3％；Ti的含量为0-0.3％，如0.1-0.3％。在某些实施方案中，当含有V和/或Ti时，V+Ti的含量之和在0.1-0.3％的范围内。
需要说明的是，在本发明所述的技术方案中，不可避免的杂质元素包括O、P和S。对于本发明的技术方案来说，O主要以氧化物夹杂存在，总氧含量高表明夹杂物较多，降低总氧含量有利于提高材料的综合性，因而对于上述不可避免的杂质元素在所述的低温压力容器用钢的质量百分比控制在：总氧≤0.001％，P≤0.010％，S≤0.005％。
进一步地，在本发明所述的低温压力容器用钢中，其化学元素还具有稀土元素，其质量百分配比≤1％，如0.1-1％。本发明中，稀土元素包括Ce、Hf、La、Re、Sc和Y。可在本发明的低温压力容器用钢中添加Ce、Hf、La、Re、Sc和Y 中的至少一种，所添加的稀土元素的总质量百分配比≤1％。
在本发明所述的技术方案中，稀土元素作为净化剂，具有脱氧和脱硫作用，从而降低氧和硫在晶界的有害影响；此外，稀土元素作为微合金化元素偏聚于晶界，起到强化晶界的作用；并且，稀土元素作为活性元素改善合金的抗氧化性能，提高表面稳定性。
进一步地，在本发明所述的低温压力容器用钢中，其微观组织中会有(Nb)CN颗粒，MgO和/或MgS颗粒和/或CaO和/或CaS颗粒，任选地含有V(C、N)颗粒和/或Ti(C、N)颗粒。
在本发明所述的低温压力容器用钢中加入选自V和Ti或其组合以及Mg和Ca或其组合的元素后，在冷却凝固过程中能促使在合金中形成少量的V(C、N)和/或Ti(C、N)以及CaO和/或MgO和/或CaS颗粒和/或MgS颗粒。上述颗粒有利于细化、稳定奥氏体晶粒，从而避免所述的低温压力容器用钢在连铸坯或热轧板表面形成裂纹缺陷，也可以改善材料低温冲击韧性。
进一步地，在本发明所述的低温压力容器用钢中，当含有V(C、N)颗粒时，这些颗粒的直径约为0.2-5μm；当含有CaO和/或CaS颗粒时，这些颗粒的直径约0.2-5μm；当含有Ti(C、N)颗粒时，这些颗粒的直径约0.1-8μm；当含有MgO和/或MgS颗粒时，这些颗粒的直径约0.1-8μm。
进一步地，在本发明所述的低温压力容器用钢中，当含有时，在所述低温压力容器用钢的截面内，V(C、N)颗粒的数量为5～20个/mm 2，CaO和/或CaS颗粒的数量为5～20个/mm 2，Ti(C、N)颗粒的数量为5～25个/mm 2，MgO和/或MgS颗粒的数量为5～25个/mm 2。当仅含有Mg和/或Ca而不含有V和/或Ti时，MgO和/或MgS颗粒和/或CaO和/或CaS的数量为15～55个/mm 2。
进一步地，在本发明所述的低温压力容器用钢中，仅含有V时，其的质量百分含量为0.1-0.2％；仅含有Ti时，其质量百分含量为0.1-0.2％；或者，当同时含有V和Ti时，两者的质量百分含量之和为0.1-0.2％。
进一步地，在本发明所述的低温压力容器用钢中，仅含有Ca时，其质量百分含量为0.001-0.003％；或者仅含有Mg时，其质量百分含量为0.001-0.003％；或者当同时含有Ca和Mg时，两者的质量百分含量之和为0.001-0.003％。
因此，在某些实施方案中，本发明的低温压力容器用钢的化学元素质量百分 配比为：
C：0.02-0.08％，优选0.02-0.06％；
Si：0.10-0.35％，优选0.1-0.3％；
Mn：0.3-0.8％，优选0.35-0.7％；
Ni：7.0-12.0％，优选7.5-10.5％；
N：≤0.005％；
Al：0.015-0.05％，优选0.02-0.04％；
Nb：0.1-0.3％，优选0.1-0.2％；
Mg：0.001-0.005％、优选0.001-0.003％，或Ca：0.001-0.005％，优选0.001-0.003％，或Mg+Ca：0.001-0.005％、优选0.001-0.003％；
任选的0.1-0.3％、优选0.1-0.2％的V；
任选的0.1-0.3％、优选0.1-0.2％的Ti；和
稀土元素：≤1％
余量为Fe和其他不可避免的杂质。
在某些实施方案中，本发明的低温压力容器用钢的化学元素质量百分配比为：
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％，或Ca：0.001-0.003％，或Mg+Ca：0.001-0.003％；
任选的0.1-0.3％、优选0.1-0.2％的V；
任选的0.1-0.3％、优选0.1-0.2％的Ti；和
稀土元素：≤1％
余量为Fe和其他不可避免的杂质。
进一步地，在本发明所述的低温压力容器用钢中，其抗拉强度≥850MPa，屈 服强度≥625MPa，延伸率≥25％，-196℃下冲击韧性≥150J。在某些实施方案中，本发明所述的低温压力容器用钢中，其抗拉强度为850-870MPa，屈服强度为625-650MPa，延伸率为25-30％，-196℃下冲击韧性为150-170J。
相应地，本发明的另一目的在于提供一种上文所述的低温压力容器用钢的制造方法，其包括步骤：
(1)冶炼：转炉冶炼，然后LF+RH精炼；
(2)连铸；
(3)热轧；
(4)淬火热处理；
(5)回火处理。
在本发明所述的制造方法中，在RH精炼末期加入少量钒铁和/或钛铁以加入V和/或Ti，并喂入钙线以加入Ca和/或加入镍镁合金以加入Mg，进一步控制钢中的各元素质量百分比满足本发明所限定的范围后，进行吹氩气的软搅拌，氩气流量控制在5～8升/分钟。
进一步地，在本发明所述的制造方法中，在热轧步骤前还具有修磨步骤。
进一步地，在本发明所述的制造方法中，在所述步骤(2)中，控制拉速控制为0.9～1.2m/min。
进一步地，在本发明所述的制造方法中，在所述步骤(2)中，连铸时采用结晶器电磁搅拌，控制电流为500-1000A，频率为2.5～3.5Hz，以使连铸后的板坯等轴晶比例≥40％。
进一步地，在本发明所述的制造方法，所述步骤(3)包括粗轧和精轧，其中，控制粗轧温度为1150～1250℃，精轧温度为1050～1150℃。
进一步地，在本发明所述的制造方法中，在所述步骤(3)中，控制总压下率为60～95％，如60～90％。
进一步地，在本发明所述的制造方法中，在所述步骤(4)中，淬火热处理温度为750～850℃，保温时间60-90min，出炉时进行水冷。
进一步地，在本发明所述的制造方法中，在所述步骤(5)中，回火处理温度为550～650℃，保温时间40-120min，出炉后空冷。上述方案的参数设置有利于提高钢的室温力学性能和低温冲击韧性，从而获得综合性能满足生产要求的热轧产 品。
本发明所述的低温压力容器用钢，采用微合金添加设计，不需要添加过多的昂贵元素，例如Ni，通过添加适量的Nb、V和/或Ti、Ca和/或Mg元素，控制较低含量的总氧，使得低温压力容器用钢具有较高的的强度、良好的成型性能以及低温冲击韧性，且钢材料成本相较于现有技术而言较低。
具体实施方式
下面将结合具体的实施例对本发明所述的低温压力容器用钢及其制造方法做进一步的解释和说明，然而该解释和说明并不对本发明的技术方案构成不当限定。
实施例1-6和对比例1-3
实施例1-6的低温压力容器用钢采用下述步骤制得：
(1)冶炼：转炉冶炼，然后LF+RH精炼，控制各化学元素的质量百分比如表3所示；
(2)连铸：控制拉速控制为0.9～1.2m/min，连铸时采用结晶器电磁搅拌，控制电流为500-1000A，频率为2.5～3.5Hz，以使连铸后的板坯等轴晶比例≥40％；
(3)热轧：包括粗轧和精轧，其中，控制粗轧温度为1150～1250℃，精轧温度为1050～1150℃，控制总压效率为60～90％；
(4)淬火热处理：温度为750～850℃，保温时间60-90min，出炉水冷；
(5)回火处理：温度为550～650℃，保温时间40-120min，出炉空冷。
需要说明的是，实施例1-6的低温压力容器用钢在热轧步骤前还具有修磨步骤。对比例1-3的对比钢采用现有技术制得。
表3列出了实施例1-6的低温压力容器用钢和对比例1-3的对比钢中各化学元素的质量百分配比。
表3：(wt％，余量为Fe和除了O、P和S之外的其他不可避免杂质元素)
Figure PCTCN2018101858-appb-000003
Figure PCTCN2018101858-appb-000004
表4列出了各实施例的制造方法的具体工艺参数。
表4
Figure PCTCN2018101858-appb-000005
对上述实施例1-6的低温压力容器用钢的微观组织进行观察，可以发现本案各实施例的微观组织从连铸板坯凝固开始到室温状态下均为奥氏体组织，而经过热轧后，采用淬火+回火(QT)热处理后本案的主要组织均为低碳回火马氏体，其中，淬火处理可获得晶粒细小的马氏体，其后的回火处理使马氏体结构又转变为铁素体和细小的析出碳化物，同时可获得少量的弥散奥氏体，该组织可以使母材 的韧性大大改善，特别适用于制造耐低温可承压的零部件。其中，各实施例的微观组织具有V(C、N)颗粒以及CaO和/或CaS颗粒，所述V(C、N)颗粒、CaO和/或CaS颗粒的直径约0.2-5μm，在所述低温压力容器用钢的截面内，V(C、N)颗粒以及CaO和/或CaS颗粒的数量为5～20个/mm 2。
此外，对实施例1-6的的低温压力容器用钢和对比例1-3的对比钢取样，对样品进行各项性能测试，将试验所获得的结果列于表5中。
表5
编号 屈服强度R el(MPa) 抗拉强度R m(MPa) 延伸率(％) -196℃冲击韧性(J)
实施例1 625 854 26 153
实施例2 632 850 25 165
实施例3 629 862 26 158
实施例4 628 858 27 161
实施例5 626 865 26 156
实施例6 627 853 28 157
对比例1 576 695 20 108
对比例2 584 734 18 105
对比例3 593 721 19 107
从表5可以看出，本案各实施例的屈服强度、抗拉强度、延伸率和-196℃下冲击韧性都显著高于各对比例的屈服强度、抗拉强度、延伸率和-196℃下冲击韧性，说明本案各实施例的力学性能和低温冲击韧性高。此外，各实施例其抗拉强度≥850MPa，屈服强度≥625MPa，延伸率≥25％，-196℃下冲击韧性≥150J。
实施例7-12
实施例7-12的低温压力容器用钢采用下述步骤制得：
(1)冶炼：转炉冶炼，然后LF+RH精炼，控制各化学元素的质量百分比如表3所示；
(2)连铸：控制拉速控制为0.9～1.2m/min，连铸时采用结晶器电磁搅拌，控制 电流为500A，频率为2.5～3.5Hz，以使连铸后的板坯等轴晶比例≥40％；
(3)热轧：包括粗轧和精轧，其中，控制粗轧温度为1150～1250℃，精轧温度为1050～1150℃，控制总压效率为60～90％；
(4)淬火热处理：温度为750～850℃，保温时间60-90min，出炉水冷；
(5)回火处理：温度为550～650℃，保温时间40-120min，出炉空冷。
需要说明的是，实施例7-12的低温压力容器用钢在热轧步骤前还具有修磨步骤。
表6列出了实施例7-12的低温压力容器用钢各化学元素的质量百分配比。
表6：(wt％，余量为Fe和除了O、P和S之外的其他不可避免杂质元素)
编号 C Si Mn Ni P S N Al Nb O Ti Mg 稀土元素
实施例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
实施例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 -
实施例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
实施例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
实施例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 -
实施例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
表7列出了各实施例的制造方法的具体工艺参数。
表7
Figure PCTCN2018101858-appb-000006
Figure PCTCN2018101858-appb-000007
对本案上述实施例7-12的低温压力容器用钢的微观组织进行观察，可以发现本案各实施例的微观组织从连铸板坯凝固开始到室温状态下均为奥氏体组织，而经过热轧后，采用淬火+回火(QT)热处理后本案的主要组织均为低碳回火马氏体，其中，淬火处理可获得晶粒细小的马氏体，其后的回火处理使马氏体结构又转变为铁素体和细小的析出碳化物，同时可获得少量的弥散奥氏体，该组织可以使母材的韧性大大改善，特别适用于制造耐低温可承压的零部件。其中，各实施例的微观组织具有Ti(C、N)颗粒以及MgO和/或MgS颗粒，所述Ti(C、N)颗粒、MgO和/或MgS颗粒的直径约0.1-8μm，在所述低温压力容器用钢的截面内，Ti(C、N)颗粒以及MgO和/或MgS颗粒的数量为5～25个/mm 2。
此外，对上述实施例7-12的低温压力容器用钢和对比例1-3的常规钢取样，进行各项性能测试，将试验所获得的结果列于表8中。
表8
编号 屈服强度R el(MPa) 抗拉强度R m(MPa) 延伸率(％) -196℃冲击韧性(J)
实施例7 635 863 27 167
实施例8 630 858 26 157
实施例9 625 857 25 163
实施例10 640 862 28 150
实施例11 638 868 29 169
实施例12 642 858 27 155
对比例1 576 695 20 108
对比例2 584 734 18 105
对比例3 593 721 19 107
从表8可以看出，本案各实施例的屈服强度、抗拉强度、延伸率和-196℃下冲击韧性都显著高于各对比例的屈服强度、抗拉强度、延伸率和-196℃下冲击韧性，说明本案各实施例的力学性能和低温冲击韧性高。此外，各实施例其抗拉强 度≥850MPa，屈服强度≥625MPa，延伸率≥25％，-196℃下冲击韧性≥150J。
实施例13-18
实施例13-18的低温压力容器用钢采用下述步骤制得：
(1)冶炼：转炉冶炼，然后LF+RH精炼，控制各化学元素的质量百分比如表3所示；
(2)连铸：控制拉速控制为0.9～1.2m/min，连铸时采用结晶器电磁搅拌，控制电流为500A，频率为2.5～3.5Hz，以使连铸后的板坯等轴晶比例≥40％；
(3)热轧：包括粗轧和精轧，其中，控制粗轧温度为1150～1250℃，精轧温度为1050～1150℃，控制总压效率为60～90％；
(4)淬火热处理：温度为750～850℃，保温时间60-90min，出炉水冷；
(5)回火处理：温度为550～650℃，保温时间40-120min，出炉空冷。
需要说明的是，实施例13-18的低温压力容器用钢在热轧步骤前还具有修磨步骤。
表9列出了实施例13-18的低温压力容器用钢各化学元素的质量百分配比。
表9.(wt％，余量为Fe和除了O、P和S之外的其他不可避免杂质元素)
编号 C Si Mn Ni P S N Al Nb O Mg
实施例13 0.04 0.10 0.5 11.0 0.008 0.004 0.002 0.015 0.10 0.0009 0.002
实施例14 0.08 0.30 0.3 9.0 0.003 0.003 0.003 0.03 0.13 0.0007 0.001
实施例15 0.06 0.22 0.7 10.0 0.007 0.004 0.004 0.035 0.28 0.0009 0.003
实施例16 0.02 0.35 0.8 7.0 0.009 0.005 0.005 0.05 0.2 0.0008 0.003
实施例17 0.05 0.28 0.4 12.0 0.006 0.002 0.004 0.04 0.3 0.0010 0.002
实施例18 0.03 0.18 0.6 8.0 0.004 0.005 0.003 0.025 0.18 0.0007 0.001
表10列出了各实施例的制造方法的具体工艺参数。
表10
Figure PCTCN2018101858-appb-000008
Figure PCTCN2018101858-appb-000009
对本案上述实施例13-18的低温压力容器用钢的微观组织进行观察，可以发现本案各实施例的微观组织从连铸板坯凝固开始到室温状态下均为奥氏体组织，而经过热轧后，采用淬火+回火(QT)热处理后本案的主要组织均为低碳回火马氏体，其中，淬火处理可获得晶粒细小的马氏体，其后的回火处理使马氏体结构又转变为铁素体和细小的析出碳化物，同时可获得少量的弥散奥氏体，该组织可以使母材的韧性大大改善，特别适用于制造耐低温可承压的零部件。其中，各实施例的微观组织具有MgO和/或MgS颗粒，所述MgO和/或MgS颗粒的直径约0.1-8μm，在所述低温压力容器用钢的截面内，MgO和/或MgS颗粒的数量为15～55个/mm 2。
此外，对上述实施例13-18的低温压力容器用钢和对比例1-3的常规钢取样，进行各项性能测试，将试验所获得的结果列于表11中。
表11
编号 屈服强度R el(MPa) 抗拉强度R m(MPa) 延伸率(％) -196℃冲击韧性(J)
实施例13 637 865 26 166
实施例14 632 856 27 159
实施例15 625 858 28 160
实施例16 643 864 25 155
实施例7 636 865 27 166
实施例18 640 859 29 157
对比例1 576 695 20 108
对比例2 584 734 18 105
对比例3 593 721 19 107
从表11可以看出，本案各实施例的屈服强度、抗拉强度、延伸率和-196℃下冲击韧性都显著高于各对比例的屈服强度、抗拉强度、延伸率和-196℃下冲击韧性，说明本案各实施例的力学性能和低温冲击韧性高。此外，各实施例其抗拉强度≥850MPa，屈服强度≥625MPa，延伸率≥25％，-196℃下冲击韧性≥150J。
需要说明的是，本发明的保护范围中现有技术部分并不局限于本申请文件所给出的实施例，所有不与本发明的方案相矛盾的现有技术，包括但不局限于在先专利文献、在先公开出版物，在先公开使用等等，都可纳入本发明的保护范围。
此外，本案中各技术特征的组合方式并不限本案权利要求中所记载的组合方式或是具体实施例所记载的组合方式，本案记载的所有技术特征可以以任何方式进行自由组合或结合，除非相互之间产生矛盾。
需要注意的是，以上列举的仅为本发明的具体实施例，显然本发明不限于以上实施例，随之有着许多的类似变化。本领域的技术人员如果从本发明公开的内容直接导出或联想到的所有变形，均应属于本发明的保护范围。

Claims (17)

  1. 一种低温压力容器用钢，其特征在于，其化学元素质量百分配比为：
    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或Ca：0.001-0.005％，或Mg+Ca：0.001-0.005％；
    V：≤0.3％；
    Ti：≤0.3％；和
    稀土元素：≤1％；
    余量为Fe和其他不可避免的杂质。
  2. 如权利要求1所述的低温压力容器用钢，其特征在于，其化学元素质量百分配比为：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 0.1-0.3％、Ca 0.001-0.005％和稀土元素≤1％，余量为Fe和其他不可避免的杂质；或其化学元素质量百分配比为：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％、Ti 0.1-0.3％、Mg 0.001-0.005％和稀土元素≤1％，余量为Fe和其他不可避免的杂质；或其化学元素质量百分配比为：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％和稀土元素≤1％，余量为Fe和其他不可避免的杂质。
  3. 如权利要求1或2所述的低温压力容器用钢，其特征在于，所述稀土元素选自Ce、Hf、La、Re、Sc和Y中的至少一种。
  4. 如权利要求1或2所述的低温压力容器用钢，其特征在于，其微观组织具有(1)MgO和/或MgS颗粒，和/或(2)CaO和/或CaS颗粒，以及任选的V(C、N)颗粒和/或Ti(C、N)颗粒。
  5. 如权利要求4所述的低温压力容器用钢，其特征在于，所述V(C、N)颗粒、CaO和/或CaS颗粒的直径约0.2-5μm；所述Ti(C、N)颗粒、MgO和/或MgS颗粒的直径约0.1-8μm。
  6. 如权利要求4所述的低温压力容器用钢，其特征在于，
    所述低温压力容器用钢含有V和Ca，在所述低温压力容器用钢的截面内，V(C、N)颗粒以及CaO和/或CaS颗粒的数量为5～20个/mm 2；或
    所述低温压力容器用钢含有Ti和Mg，Ti(C、N)颗粒以及MgO和/或MgS颗粒的数量为5～25个/mm 2；或
    所述低温压力容器用钢含有Mg，不含有Ca、Ti和V，MgO和/或MgS颗粒的数量为15～55个/mm 2。
  7. 如权利要求2所述的低温压力容器用钢，其特征在于，V的质量百分配比为0.1-0.2％；Ti的质量百分配比为0.1-0.2％。
  8. 如权利要求2所述的低温压力容器用钢，其特征在于，Ca的质量百分配比为0.001-0.003％；Mg的质量百分配比为0.001-0.003％。
  9. 如权利要求1所述的低温压力容器用钢，其特征在于，其抗拉强度≥850MPa，屈服强度≥625MPa，延伸率≥25％，-196℃下冲击韧性≥150J。
  10. 如权利要求1-9中任意一项所述的低温压力容器用钢的制造方法，其特征在于，包括步骤：
    (1)冶炼：转炉冶炼，然后LF+RH精炼；
    (2)连铸；
    (3)热轧；
    (4)淬火热处理；
    (5)回火处理。
  11. 如权利要求10所述的制造方法，其特征在于，在热轧步骤前还具有修磨步骤。
  12. 如权利要求10或11所述的制造方法，其特征在于，在所述步骤(2)中，控制拉速控制为0.9～1.2m/min。
  13. 如权利要求9或10所述的制造方法，其特征在于，在所述步骤(2)中，连铸时采用结晶器电磁搅拌，控制电流为500-1000A，频率为2.5～3.5Hz，以使 连铸后的板坯等轴晶比例≥40％。
  14. 如权利要求10或11所述的制造方法，其特征在于，所述步骤(3)包括粗轧和精轧，其中，控制粗轧温度为1150～1250℃，精轧温度为1050～1150℃。
  15. 如权利要求10或11所述的制造方法，其特征在于，在所述步骤(3)中，控制总压下率为60～95％。
  16. 如权利要求10或11所述的制造方法，其特征在于，在所述步骤(4)中淬火热处理温度为750～850℃，保温时间60-90min，出炉时进行水冷。
  17. 如权利要求10或11所述的制造方法，其特征在于，在所述步骤(5)中，回火处理温度为550～650℃，保温时间40-120min，出炉后空冷。
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