WO2020237975A1 - 一种LNG储罐用7Ni钢板及生产工艺 - Google Patents

一种LNG储罐用7Ni钢板及生产工艺 Download PDF

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WO2020237975A1
WO2020237975A1 PCT/CN2019/111410 CN2019111410W WO2020237975A1 WO 2020237975 A1 WO2020237975 A1 WO 2020237975A1 CN 2019111410 W CN2019111410 W CN 2019111410W WO 2020237975 A1 WO2020237975 A1 WO 2020237975A1
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rolling
steel plate
rolled
air cooling
casting
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PCT/CN2019/111410
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English (en)
French (fr)
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黄一新
谢章龙
伍会滨
霍松波
张鹏程
张丙军
李庆春
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南京钢铁股份有限公司
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Priority to KR1020217040526A priority Critical patent/KR20220004220A/ko
Priority to JP2021569882A priority patent/JP7340627B2/ja
Publication of WO2020237975A1 publication Critical patent/WO2020237975A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—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
    • 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
    • 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
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—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
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the invention relates to the technical field of steel smelting, in particular to a 7Ni steel plate for LNG storage tanks and a production process.
  • 201310285597.4 A high-nickel steel for ultra-low temperature pressure vessel and its manufacturing method involves a steel with a Ni mass fraction of 7.00% to 7.50%.
  • the 7Ni steel plate obtained by the twice quenching + tempering process can replace 9Ni steel.
  • Application No. 201310494688.9 A low Ni and high Mn economical low temperature steel and its manufacturing method that can be used at -196°C” involves a steel with a Mn mass fraction of 1.00% to 1.50%, and a Ni mass fraction of 7.00% to 8.00%. Using two quenching and tempering processes, the Ni steel obtained has excellent toughness at -196°C.
  • the application number 201410369201.9 "low-cost ultra-low temperature nickel steel and its manufacturing method" adopts normalizing + quenching + tempering process to obtain Ni steel with excellent toughness at -196°C.
  • the UFC+TMCP process is used to directly cool the steel plate to below the martensite transformation temperature after rolling to replace the offline quenching process, simplify the heat treatment process, and improve the low temperature toughness of the 7Ni steel plate.
  • the present invention overcomes the shortcomings of the prior art and provides a 7Ni steel plate for LNG storage tanks and a production process. Under the premise of ensuring the performance of the steel for LNG storage, the Ni content is reduced as much as possible, and a Economical and feasible preparation method.
  • the present invention provides a 7Ni steel plate for LNG storage tanks, the chemical composition and mass percentage are as follows: C: 0.02% ⁇ 0.06%, Si: 0.20% ⁇ 0.35%, Ni: 4.0% ⁇ 8.0%, Mn: 0.3% ⁇ 0.7%, P ⁇ 0.005%, S ⁇ 0.005%, Al: 0.03% ⁇ 0.05%, Nb: 0.02% ⁇ 0.05%, Cr: 0.2% ⁇ 0.4%, the balance is Fe and unavoidable impurities .
  • the present invention adopts the design of Nb, Cr microalloyed Ni-type alloy, and innovates a normalizing rolling + two-phase zone quenching + tempering production process, eliminating the rapid cooling process after rolling, and not only saving energy , And provide a good plate shape for the smooth implementation of the subsequent quenching process, and finally obtain the LNG storage tank steel with excellent mechanical properties.
  • the thickness is 8-30 mm.
  • Another object of the present invention is to provide a 7Ni steel plate production process for LNG storage tanks, including
  • Casting billet preparation smelting raw materials according to chemical composition, smelting in a vacuum smelting furnace, casting into ingots, then forging the ingots into square billets, and air cooling in a sheltered place;
  • the casting slab is kept at 1150 ⁇ 1250°C for 2 ⁇ 3h; the casting slab is rolled in two stages, in which the opening temperature of rough rolling is 1000 ⁇ 1100°C, and the total reduction ratio is 40% ⁇ 60%.
  • the start rolling temperature of the finishing rolling is 850 ⁇ 900°C, the total reduction ratio is 40% ⁇ 70%, the final rolling temperature is 750 ⁇ 850°C, and then air cooling;
  • Two-phase zone quenching + tempering Quench the rolled steel plate at 600-700°C to below 300°C, and then temper at 500-580°C, tempering rate of 5-20°C/s, holding time for 0.5-2h, Air cooling.
  • the aforementioned 7Ni steel plate production process for LNG storage tanks, the chemical composition and mass percentage of the steel plate are as follows: C: 0.05%, Si: 0.25%, Mn: 0.60%, Ni: 7.2%, P: 0.0045%, S : 0.0030%, Al: 0.038%, Cr: 0.28%, Nb: 0.043%, the balance is Fe and unavoidable impurities;
  • Casting billet preparation smelting raw materials according to chemical composition, smelting in a vacuum smelting furnace, casting into ingots, then forging the ingots into a square billet with a thickness of 80mm, and air cooling in a sheltered place;
  • Normalizing rolling send the cast slab to a heating furnace, heat it to 1156°C, hold for 2.6 hours, and take it out for rolling; the cast slab is rolled in two stages, in which the rough rolling is rolled in the austenite completely recrystallized zone.
  • the start-rolling temperature is 1100°C
  • the reduction is 60%
  • the finish rolling is rolled in the austenite non-recrystallization zone
  • the start-rolling temperature is 900°C
  • the reduction is 63%
  • the final rolling temperature is 790°C
  • air cooling Form 12mm thick hot-rolled steel plate rolling
  • Quenching in two-phase zone + tempering Quench the rolled steel plate at 660°C to below 300°C, and then temper at 560°C at a tempering rate of 10°C/s, heat preservation for 1 hour, and air cooling.
  • the aforementioned 7Ni steel plate production process for LNG storage tanks, the chemical composition and mass percentage of the steel plate are as follows: C: 0.06%, Si: 0.23%, Mn: 0.55%, Ni: 7.3%, P: 0.0043%, S : 0.0031%, Al: 0.035%, Cr: 0.25%, Nb: 0.040%, the balance is Fe and unavoidable impurities;
  • Casting billet preparation smelting raw materials according to chemical composition, smelting in a vacuum smelting furnace, casting into ingots, then forging the ingots into a square billet with a thickness of 80mm, and air cooling in a sheltered place;
  • Normalizing rolling send the cast slab to a heating furnace, heat it to 1239°C, hold for 2.1h, and take it out for rolling; the cast slab is rolled in two stages, in which the rough rolling is rolled in the austenite completely recrystallized zone.
  • the opening temperature is 1100°C
  • the reduction is 60%
  • the finish rolling is rolled in the austenite unrecrystallized zone
  • the opening temperature is 900°C
  • the reduction is 45%
  • the final rolling temperature is 790°C
  • air cooling Form 18mm thick hot-rolled steel plate rolling
  • Two-phase zone quenching + tempering quench the rolled steel plate at 660°C to below 300°C, then temper at 560°C, tempering rate of 10°C/s, heat preservation for 1h, air cooling.
  • nickel is a non-carbide forming element, which can expand the ⁇ phase region, is an austenite forming and stabilizing element, and improves low temperature toughness without reducing strength; nickel can shift the CCT curve of steel to the right, Thereby reducing the critical quenching speed and improving the hardenability; nickel also has an important effect of improving low temperature toughness and reducing the ductile-brittle transition temperature, so Ni is the most important alloying element of the present invention;
  • carbon is a strong solid solution strengthening element and a strong austenite stabilizing element. It has a positive effect on the strength of the steel plate, but has an adverse effect on the toughness, plasticity and welding performance. Therefore, in order to make the low temperature steel plate It has good impact toughness and welding performance, and the carbon content needs to be controlled in a low range;
  • manganese mainly plays a role of solid solution strengthening, which can compensate for the decrease in strength caused by the reduction of carbon content; at the same time, manganese, like nickel, can reduce the phase transition temperature of steel and appropriately increase Mn/C and Mn/S Conducive to the improvement of toughness, so the present invention uses Mn as one of the main alloying elements;
  • silicon is a solid solution strengthening element and a deoxidizing element, which can increase the strength of steel and reduce the content of harmful element oxygen in the steelmaking process; in addition to silicon and manganese in a certain proportion, it exists in the steel to inhibit manganese segregation. In addition, it can also inhibit the segregation of phosphorus in the grain boundary, but silicon will deteriorate the low-temperature toughness of the welding heat-affected zone of steel, so the silicon content is controlled at 0.15-0.3%;
  • chromium in the present invention can improve the hardenability of the steel plate and increase the strength of the steel plate; adding a small amount of Nb and controlling a certain Nb/Si range is not only harmless to the strength and plasticity, but also helps to improve the wide and thick plates
  • the welding performance of steel; S and P are harmful elements in steel, which are easy to cause segregation, reduce the low temperature toughness of steel, and increase the sensitivity of hot cracking during welding. Therefore, the content of P and S in steel must be strictly controlled;
  • the cross-sectional structure of the present invention is that martensite and rotating austenite are distributed on the ferrite matrix; the mechanical properties are: the yield strength is 590-700MPa, the tensile strength is 690-790MPa, and the elongation is ⁇ 24% , The transverse impact energy at -196°C is ⁇ 100J.
  • Figure 1 is a metallographic photo of Example 1
  • Figure 2 is a metallographic photo of Example 2.
  • This embodiment provides a 7Ni steel plate for LNG storage tank and its production process.
  • the chemical composition and mass percentage of the steel plate are as follows: C: 0.05%, Si: 0.25%, Mn: 0.60%, Ni: 7.2%, P: 0.0045% , S: 0.0030%, Al: 0.038%, Cr: 0.28%, Nb: 0.043%, the balance is Fe and unavoidable impurities.
  • Billet preparation smelting raw materials according to chemical composition, smelting in a vacuum smelting furnace, casting into an ingot, then forging the ingot into a square billet with a thickness of 80mm, and air cooling in a sheltered place.
  • Normalizing rolling send the cast slab to a heating furnace, heat it to 1156°C, hold for 2.6 hours, and take it out for rolling; the cast slab is rolled in two stages, in which the rough rolling is rolled in the austenite completely recrystallized zone.
  • the start-rolling temperature is 1100°C
  • the reduction is 60%
  • the finish rolling is rolled in the austenite non-recrystallization zone
  • the start-rolling temperature is 900°C
  • the reduction is 63%
  • the final rolling temperature is 790°C
  • air cooling Form a 12mm thick hot rolled steel sheet.
  • Quenching in two-phase zone + tempering Quench the rolled steel plate at 660°C to below 300°C, and then temper at 560°C at a tempering rate of 10°C/s, heat preservation for 1 hour, and air cooling.
  • This embodiment provides a 7Ni steel plate for LNG storage tank and its production process.
  • the chemical composition and mass percentage of the steel plate are as follows: C: 0.06%, Si: 0.23%, Mn: 0.55%, Ni: 7.3%, P: 0.0043% , S: 0.0031%, Al: 0.035%, Cr: 0.25%, Nb: 0.040%, the balance is Fe and unavoidable impurities.
  • Billet preparation smelt raw materials according to chemical composition, smelt in a vacuum smelting furnace, cast into ingots, then forge the ingots into square billets with a thickness of 80mm, and cool in air in a sheltered place.
  • Normalizing rolling send the cast slab to a heating furnace, heat it to 1239°C, hold for 2.1h, take it out for rolling; carry out two-stage rolling on the cast slab, in which the rough rolling is rolled in the austenite completely recrystallized zone.
  • the opening temperature is 1100°C
  • the reduction is 60%
  • the finish rolling is rolled in the austenite non-recrystallization zone
  • the opening temperature is 900°C
  • the reduction is 45%
  • the final rolling temperature is 790°C
  • air cooling Rolld into 18mm thick hot-rolled steel sheet.
  • Quenching in two-phase zone + tempering Quench the rolled steel plate at 660°C to below 300°C, and then temper at 560°C at a tempering rate of 10°C/s, heat preservation for 1 hour, and air cooling.
  • the present invention adopts a nickel-reducing alloy design and adopts a normalizing rolling + two-phase zone quenching + tempering production process, and its performance fully meets the GB 3531-2014 9Ni standard in low-temperature pressure vessel steel. Greatly reduce production costs.
  • the present invention may also have other embodiments. All technical solutions formed by equivalent replacements or equivalent transformations fall within the protection scope of the present invention.

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Abstract

一种LNG储罐用7Ni钢板及生产工艺，涉及钢铁冶炼技术领域，其化学成分及质量百分比如下：C：0.02％～0.06％，Si：0.20％～0.35％，Ni：4.0％～8.0％，Mn：0.3％～0.7％，P≤0.005％，S≤0.005％，Al：0.03％～0.05％，Nb：0.02％～0.05％，Cr：0.2％～0.4％，余量为Fe和不可避免杂质。钢板抗拉强度690～790Mpa，屈服强度590～700MPa，延伸率≥24％，-196℃下的横向冲击功在≥100J，可用于制造储存和运输LNG的压力容器等。

Description

一种LNG储罐用7Ni钢板及生产工艺 技术领域
本发明涉及钢铁冶炼技术领域，特别是涉及一种LNG储罐用7Ni钢板及生产工艺。
背景技术
随着经济的发展，环境和资源问题日益成为各国发展的重中之重，LNG作为一种清洁、无污染、产热量高的能源，未来将逐步在能源使用中占据更大比例，扩大对天然气的使用范围成为我国优化能源结构和保护生态环境的重要手段。目前，国内外广泛用于LNG储存、运输工具中的钢板为9Ni钢，我国作为贫Ni国家，为了节约成本，在确保性能的基础上降低Ni含量是重要途径之一。含量节镍型7Ni钢的相关研究还处于起步阶段，目前已有少量关于7Ni钢板的专利，申请号201711306269.2的“一种用于超低温环境的节镍型7Ni钢及其热处理工艺的制作方法”公开了一种用于超低温环境的节镍型7Ni钢及其热处理工艺，7Ni钢成分：Ni：7.00％～7.60％，C：0.02％～0.06％，Si：0.03％～0.80％，Mn：0.10％～0.90％，Cr：0.30％～0.60％，余量为Fe及不可避免的夹杂，该采用QLT热处理的7Ni钢具有优良强塑性组合和出色的低温韧性，其性能已经达到9Ni钢相当水平。申请号201310285597.4的“一种超低温压力容器用高镍钢及其制造方法”所涉及钢的Ni质量分数为7.00％～7.50％，采用两次淬火+回火工艺得到的7Ni钢板可以替代9Ni钢用于制造LNG储罐。申请号201310494688.9的“一种可用于-196℃的低Ni高Mn经济型低温钢及其制造方法”所涉及钢的Mn质量分数为1.00％～1.50％，Ni质量分数为7.00％～8.00％，采用两次淬火加回火工艺，得到的Ni钢在-196℃韧性优异。申请号201410369201.9的“低成本超低温镍钢及其制造方法”采用正火+淬火+回火工艺，得到-196℃韧性优异的Ni钢。还有采用UFC+TMCP工艺，轧后直接将钢板快速冷却至马氏体转变温度以下替代离线淬火工艺，简化热处理工序的方法， 提高7Ni钢板的低温韧性。
发明内容
本发明针对上述技术问题，克服现有技术的缺点，提供一种LNG储罐用7Ni钢板及生产工艺，在保证LNG储运用钢的性能的前提下，尽可能降低Ni的含量，提供一种经济且可行的制备方法。
为了解决以上技术问题，本发明提供一种LNG储罐用7Ni钢板，其化学成分及质量百分比如下：C：0.02％～0.06％，Si：0.20％～0.35％，Ni：4.0％～8.0％，Mn：0.3％～0.7％，P≤0.005％，S≤0.005％，Al：0.03％～0.05％，Nb：0.02％～0.05％，Cr：0.2％～0.4％，余量为Fe和不可避免杂质。
技术效果：本发明采用Nb、Cr微合金化节Ni型合金设计，创新了一种正火轧制+两相区淬火+回火生产工艺，免去了轧后快速冷却过程，不仅节约了能源，而且为后续淬火工艺顺利实施提供了良好的板形，最终获得了力学性能优异的LNG储罐钢。
本发明进一步限定的技术方案是：
进一步的，厚度为8～30mm。
本发明的另一目的在于提供一种LNG储罐用7Ni钢板生产工艺，包括
铸坯制备：按化学组成配成冶炼原料，在真空冶炼炉中进行冶炼，浇铸成铸锭，然后将铸锭锻压成方形铸坯，在避风处空冷；
正火轧制：将铸坯在1150～1250℃保温2～3h；对铸坯进行两阶段轧制，其中粗轧的开轧温度为1000～1100℃，总压缩比为40％～60％，精轧的开轧温度为850～900℃，总压缩比为40％～70％，终轧温度750～850℃，然后空冷；
两相区淬火+回火：将轧制后的钢板在600～700℃淬火至300℃以下，再在500～580℃回火，回火速率为5～20℃/s，保温0.5～2h，空冷。
前所述的一种LNG储罐用7Ni钢板生产工艺，钢板的化学成分及质量百分 比如下：C：0.05％，Si：0.25％，Mn：0.60％，Ni：7.2％，P：0.0045％，S：0.0030％，Al：0.038％，Cr：0.28％，Nb：0.043％，余量为Fe和不可避免杂质；
铸坯制备：按化学组成配成冶炼原料，在真空冶炼炉中进行冶炼，浇铸成铸锭，然后将铸锭锻压成厚度为80mm的方形铸坯，在避风处空冷；
正火轧制：将铸坯送至加热炉，加热至1156℃，保温2.6h，取出进行轧制；对铸坯进行两阶段轧制，其中粗轧在奥氏体完全再结晶区轧制，开轧温度为1100℃，压下量为60％，精轧在奥氏体未再结晶区轧制，开轧温度为900℃，压下量为63％，终轧温度790℃，然后空冷，形成12mm厚热轧钢板轧；
两相区淬火+回火：将轧制后的钢板在660℃淬火至300℃以下，再在560℃回火，回火速率为10℃/s，保温1h，空冷。
前所述的一种LNG储罐用7Ni钢板生产工艺，钢板的化学成分及质量百分比如下：C：0.06％，Si：0.23％，Mn：0.55％，Ni：7.3％，P：0.0043％，S：0.0031％，Al：0.035％，Cr：0.25％，Nb：0.040％，余量为Fe和不可避免杂质；
铸坯制备：按化学组成配成冶炼原料，在真空冶炼炉中进行冶炼，浇铸成铸锭，然后将铸锭锻压成厚度为80mm的方形铸坯，在避风处空冷；
正火轧制：将铸坯送至加热炉，加热至1239℃，保温2.1h，取出进行轧制；对铸坯进行两阶段轧制，其中粗轧在奥氏体完全再结晶区轧制，开轧温度为1100℃，压下量为60％，精轧在奥氏体未再结晶区轧制，开轧温度为900℃，压下量为45％，终轧温度790℃，然后空冷，形成18mm厚热轧钢板轧；
两相区淬火+回火：将轧制后的钢板在660℃淬火至300℃以下，再在560℃回火，回火速率为10℃/s，保温1h，空冷。
本发明的有益效果是：
(1)本发明中镍为非碳化物形成元素，可扩大γ相区，是奥氏体形成和稳 定元素，在不降低强度的情况下提高低温韧性；镍可以使钢的CCT曲线右移，从而降低临界淬火速度，提高淬透性；镍还有提高低温韧性降低韧-脆转变温度的重要作用，因此Ni是本发明的最主要合金化元素；
(2)本发明中碳是强固溶强化元素，也是强奥氏体稳定化元素，对钢板的强度有着积极的影响，但是对韧、塑性及焊接性能有着不利的影响，因此，为了使低温钢板具有很好的冲击韧性和焊接性能，需将碳含量控制在较低的范围；
(3)本发明中锰主要起固溶强化的作用，可以弥补碳含量减少产生的强度的下降；同时锰同镍一样，能使钢的相变温度降低，适当提高Mn/C和Mn/S有利于韧性的改善，因此本发明将Mn作为主要的合金元素之一；
(4)本发明中硅是固溶强化元素和脱氧元素，可以提高钢的强度，在炼钢过程中可降低有害元素氧的含量；硅除了和锰按一定比例存在于钢中抑制锰偏聚外，还可以抑制磷在晶界偏聚，但是硅会使钢的焊接热影响区低温韧性恶化，因此硅含量控制在0.15～0.3％；
(5)本发明中铬的加入可以提高钢板的淬透性，提高钢板的强度；加入微量的Nb，并控制一定的Nb/Si范围，不仅对强度和塑性无害，而且有利于提高宽厚板的焊接性能；S和P是钢中的有害元素，易导致偏析，降低钢的低温韧性，增加焊接时的热裂纹敏感性，故要严格控制钢中P、S的含量；
(6)本发明的断面组织为铁素体基体上分布着马氏体和回转奥氏体；力学性能指标为：屈服强度在590～700MPa，抗拉强度在690～790MPa，延伸率≥24％，在-196℃下的横向冲击功在≥100J。
附图说明
图1为实例1金相照片；
图2为实例2金相照片。
具体实施方式
实施例1
本实施例提供的一种LNG储罐用7Ni钢板及生产工艺，钢板的化学成分及质量百分比如下：C：0.05％，Si：0.25％，Mn：0.60％，Ni：7.2％，P：0.0045％，S：0.0030％，Al：0.038％，Cr：0.28％，Nb：0.043％，余量为Fe和不可避免杂质。
铸坯制备：按化学组成配成冶炼原料，在真空冶炼炉中进行冶炼，浇铸成铸锭，然后将铸锭锻压成厚度为80mm的方形铸坯，在避风处空冷。
正火轧制：将铸坯送至加热炉，加热至1156℃，保温2.6h，取出进行轧制；对铸坯进行两阶段轧制，其中粗轧在奥氏体完全再结晶区轧制，开轧温度为1100℃，压下量为60％，精轧在奥氏体未再结晶区轧制，开轧温度为900℃，压下量为63％，终轧温度790℃，然后空冷，形成12mm厚热轧钢板轧。
两相区淬火+回火：将轧制后的钢板在660℃淬火至300℃以下，再在560℃回火，回火速率为10℃/s，保温1h，空冷。
本实例得到的低温钢板按照相关国家标准进行检测，检测结果见表1。
表1：实例1低温钢板性能
Figure PCTCN2019111410-appb-000001
实施例2
本实施例提供的一种LNG储罐用7Ni钢板及生产工艺，钢板的化学成分及质量百分比如下：C：0.06％，Si：0.23％，Mn：0.55％，Ni：7.3％，P：0.0043％，S：0.0031％，Al：0.035％，Cr：0.25％，Nb：0.040％，余量为Fe和不可避免杂质。
铸坯制备：按化学组成配成冶炼原料，在真空冶炼炉中进行冶炼，浇铸成 铸锭，然后将铸锭锻压成厚度为80mm的方形铸坯，在避风处空冷。
正火轧制：将铸坯送至加热炉，加热至1239℃，保温2.1h，取出进行轧制；对铸坯进行两阶段轧制，其中粗轧在奥氏体完全再结晶区轧制，开轧温度为1100℃，压下量为60％，精轧在奥氏体未再结晶区轧制，开轧温度为900℃，压下量为45％，终轧温度790℃，然后空冷，形成18mm厚热轧钢板轧。
两相区淬火+回火：将轧制后的钢板在660℃淬火至300℃以下，再在560℃回火，回火速率为10℃/s，保温1h，空冷。
本实例得到的低温钢板按照相关国家标准进行检测，检测结果见表2。
表2：实例2低温钢板性能
Figure PCTCN2019111410-appb-000002
本发明与现有技术相比，通过减镍的合金设计，采用正火轧制+两相区淬火+回火生产工艺，在性能上完全达到GB 3531-2014低温压力容器用钢中9Ni标准，大大降低生产成本。
除上述实施例外，本发明还可以有其他实施方式。凡采用等同替换或等效变换形成的技术方案，均落在本发明要求的保护范围。

Claims (5)

  1. 一种LNG储罐用7Ni钢板，其特征在于，其化学成分及质量百分比如下：C：0.02％～0.06％，Si：0.20％～0.35％，Ni：4.0％～8.0％，Mn：0.3％～0.7％，P≤0.005％，S≤0.005％，Al：0.03％～0.05％，Nb：0.02％～0.05％，Cr：0.2％～0.4％，余量为Fe和不可避免杂质。
  2. 根据权利要求1所述的一种LNG储罐用7Ni钢板，其特征在于：厚度为8～30mm。
  3. 一种LNG储罐用7Ni钢板生产工艺，其特征在于：包括
    铸坯制备：按化学组成配成冶炼原料，在真空冶炼炉中进行冶炼，浇铸成铸锭，然后将铸锭锻压成方形铸坯，在避风处空冷；
    正火轧制：将铸坯在1150～1250℃保温2～3h；对铸坯进行两阶段轧制，其中粗轧的开轧温度为1000～1100℃，总压缩比为40％～60％，精轧的开轧温度为850～900℃，总压缩比为40％～70％，终轧温度750～850℃，然后空冷；
    两相区淬火+回火：将轧制后的钢板在600～700℃淬火至300℃以下，再在500～580℃回火，回火速率为5～20℃/s，保温0.5～2h，空冷。
  4. 根据权利要求3所述的一种LNG储罐用7Ni钢板生产工艺，其特征在于：
    钢板的化学成分及质量百分比如下：C：0.05％，Si：0.25％，Mn：0.60％，Ni：7.2％，P：0.0045％，S：0.0030％，Al：0.038％，Cr：0.28％，Nb：0.043％，余量为Fe和不可避免杂质；
    铸坯制备：按化学组成配成冶炼原料，在真空冶炼炉中进行冶炼，浇铸成铸锭，然后将铸锭锻压成厚度为80mm的方形铸坯，在避风处空冷；
    正火轧制：将铸坯送至加热炉，加热至1156℃，保温2.6h，取出进行轧制；对铸坯进行两阶段轧制，其中粗轧在奥氏体完全再结晶区轧制，开轧温度为1100℃，压下量为60％，精轧在奥氏体未再结晶区轧制，开轧温度 为900℃，压下量为63％，终轧温度790℃，然后空冷，形成12mm厚热轧钢板轧；
    两相区淬火+回火：将轧制后的钢板在660℃淬火至300℃以下，再在560℃回火，回火速率为10℃/s，保温1h，空冷。
  5. 根据权利要求3所述的一种LNG储罐用7Ni钢板生产工艺，其特征在于：
    钢板的化学成分及质量百分比如下：C：0.06％，Si：0.23％，Mn：0.55％，Ni：7.3％，P：0.0043％，S：0.0031％，Al：0.035％，Cr：0.25％，Nb：0.040％，余量为Fe和不可避免杂质；
    铸坯制备：按化学组成配成冶炼原料，在真空冶炼炉中进行冶炼，浇铸成铸锭，然后将铸锭锻压成厚度为80mm的方形铸坯，在避风处空冷；
    正火轧制：将铸坯送至加热炉，加热至1239℃，保温2.1h，取出进行轧制；对铸坯进行两阶段轧制，其中粗轧在奥氏体完全再结晶区轧制，开轧温度为1100℃，压下量为60％，精轧在奥氏体未再结晶区轧制，开轧温度为900℃，压下量为45％，终轧温度790℃，然后空冷，形成18mm厚热轧钢板轧；
    两相区淬火+回火：将轧制后的钢板在660℃淬火至300℃以下，再在560℃回火，回火速率为10℃/s，保温1h，空冷。
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